Methods of making an elastomer composite reinforced with silica and products containing same

ABSTRACT

Methods to make a silica elastomer composite with a destabilized dispersion of silica are described, along with silica elastomer composites made from the methods. The advantages achieved with the methods are further described.

The present invention relates to methods of making silica elastomercomposites. More particularly, the present invention relates to a silicareinforced elastomer composite formed by a wet masterbatch method.

Numerous products of commercial significance are formed of elastomericcompositions wherein particulate reinforcing material is dispersed inany of various synthetic elastomers, natural rubber or elastomer blends.Carbon black and silica, for example, are widely used as reinforcingagents in natural rubber and other elastomers. It is common to produce amasterbatch, that is, a premixture of reinforcing material, elastomer,and various optional additives, such as extender oil. Numerous productsof commercial significance are formed of such elastomeric compositions.Such products include, for example, vehicle tires wherein differentelastomeric compositions may be used for the tread portion, sidewalls,wire skim and carcass. Other products include, for example, engine mountbushings, conveyor belts, windshield wipers, seals, liners, wheels,bumpers, and the like.

Good dispersion of particulate reinforcing agents in rubber compoundshas been recognized for some time as one of the most importantobjectives for achieving good quality and consistent productperformance, and considerable effort has been devoted to the developmentof methods to improve dispersion quality. Masterbatch and other mixingoperations have a direct impact on mixing efficiency and on dispersionquality. In general, for instance, when carbon black is employed toreinforce rubber, acceptable carbon black macro-dispersions can often beachieved in a dry-mixed masterbatch. However, high quality, uniformdispersion of silica by dry-mix processes poses difficulties, andvarious solutions have been offered by the industry to address thisproblem, such as precipitated silica in the form of “highly dispersiblesilica” or “HDS” flowable granules. More intensive mixing can improvesilica dispersion, but also can degrade the elastomer into which thefiller is being dispersed. This is especially problematic in the case ofnatural rubber, which is highly susceptible to mechanical/thermaldegradation.

In addition to dry mixing techniques, it is known to feed elastomerlatex or polymer solution and a carbon black or silica slurry to anagitated tank. Such “wet masterbatch” techniques can be used withnatural rubber latex and emulsified synthetic elastomers, such asstyrene butadiene rubber (SBR). However, while this wet technique hasshown promise when the filler is carbon black, this wet technique, whenthe filler is silica, poses challenges to achieving acceptable elastomercomposite. Specific techniques for producing wet masterbatch, such asthe one disclosed in U.S. Pat. No. 6,048,923, the contents of which areincorporated by reference herein, have not been effective for producingelastomer composites employing silica particles as the sole or principalreinforcing agent.

Accordingly, there is a need to improve methods that incorporate silicain elastomer composites in a wet masterbatch process, such as one thatmakes use of combining two fluids together under continuous, high energyimpact conditions, so as to achieve an acceptable elastomer compositecomprising silica particles as the sole or principal reinforcing agent.

SUMMARY OF THE PRESENT INVENTION

A feature of the present invention is to provide methods to produceelastomer composites using a wet masterbatch process which permits theuse of silica, and yet achieves desirable silica elastomer composites.

To achieve these and other advantages, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention relates to the controlled and selectiveplacement or introduction of silica in a wet masterbatch process thatforms an elastomer composite.

The present invention relates to a method of making an elastomercomposite in a wet masterbatch process that includes, but is not limitedto, the use of a fluid that includes an elastomer latex, and the use ofan additional fluid that includes a destabilized dispersion ofparticulate silica. The two fluids are combined together undercontinuous flow conditions and selected velocities. The combining issuch that the silica is dispersed within the elastomer latex and, inparallel (or almost parallel), the elastomer latex is transformed from aliquid to a solid or semi-solid elastomer composite, such as to a solidor semi-solid silica-containing continuous rubber phase. This can occur,for instance, in about two seconds or less such as a fraction of asecond, due to the one fluid impacting the other fluid with sufficientenergy to cause the uniform and intimate distribution of silicaparticles in the elastomer. The use of a destabilized dispersion ofsilica in this masterbatch process enables formation of an elastomercomposite with desirable properties.

The present invention further relates to elastomer composites formedfrom any one or more of the processes of the present invention. Thepresent invention also relates to articles that are made from or includethe elastomer composite(s) of the present invention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide a further explanation of the presentinvention as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this application, illustrate various features of the presentinvention and, together with the description, serve to explain theprinciples of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates an exemplary mixing apparatus in accordance withProcess A;

FIG. 1B illustrates an exemplary mixing apparatus in accordance withProcess B;

FIG. 1C illustrates an exemplary mixing apparatus having an additionalinlet, in accordance with Process B; and

FIG. 2 is a block diagram of various steps that can occur in theformation of the elastomer composite according to embodiments of thepresent invention and in making rubber compounds with such elastomercomposites.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to the selective and strategicintroduction of silica into an elastomer latex in a continuous, rapid,wet masterbatch process. This process can be carried out in asemi-confined reaction zone, such as a tubular mixing chamber or othermixing chamber of an apparatus suitable for carrying out such a processunder controlled volumetric flow and velocity parameters, leading tobeneficial properties that would not be achieved, but for this selectiveand strategic use of silica. As explained in further detail herein, by‘selective’, the present invention uses a destabilized dispersion ofsilica. And, by ‘strategic’ introduction, the present invention uses atleast two separate fluids, one fluid that includes an elastomer latex,and another fluid that includes the destabilized dispersion of silica.The two fluids can be pumped or transferred into a reaction zone, suchas a semi-confined reaction zone. The two fluids can be combined undercontinuous flow conditions, and under selected volumetric flow andvelocity conditions. The combining under pressure with selecteddifferential velocity conditions is sufficiently energetic that thesilica can be distributed in two seconds or less, such as inmilliseconds, within the elastomer latex, and the elastomer latex istransformed from a liquid to a solid phase, such as to a silicaelastomer composite in the form of a solid or semi-solidsilica-containing continuous rubber phase.

The present invention relates in part, to a method of producing a silicaelastomer composite, comprising, consisting essentially of, consistingof, or including:

-   -   (a) providing a continuous flow under pressure of at least a        first fluid comprising a destabilized dispersion of silica and        providing a continuous flow of a second fluid comprising        elastomer latex;    -   (b) adjusting volumetric flows of the first fluid and the second        fluid to yield an elastomer composite having a silica content of        from about 15 phr to about 180 phr; and    -   (c) combining the first fluid flow and the second fluid flow        (for instance in a semi-confined reaction zone) with sufficient        impact to distribute the silica within the elastomer latex, to        obtain a flow of a solid silica-containing continuous rubber        phase or semi-solid silica-containing continuous rubber phase.        The method transforms the elastomer latex from a liquid to a        flow of a solid or semi-solid silica-containing continuous        rubber phase. The silica-containing continuous rubber phase can        be recovered as a substantially continuous flow of the solid or        semi-solid silica-containing continuous rubber phase.

Further details and/or options for the methods of the present inventionare described below.

As used herein, “silica” means particulate silicon dioxide, or aparticle coated with silicon dioxide, and includes precipitated silicain any form, such as highly dispersible (HDS) granules, non-HDSgranules, silica aggregates and silica particles; colloidal silica;fumed silica; and any combinations thereof. Such silicon dioxide orsilicon dioxide coated particles may have been chemically treated toinclude functional groups bonded (attached (e.g., chemically attached)or adhered (e.g., adsorbed)) to the silica surface. Thus, “silica”includes any particle having a surface substantially consisting ofsilica or silica having functional groups bonded or attached to it.

As used herein, “dispersion” means a stable suspension of solidparticles in aqueous fluid, wherein the charge at the surface of theparticles prevents particle agglomeration and the dispersion ischaracterized by a zeta potential magnitude of greater than or equal to30 mV.

Zeta potential is used to measure stability of charged particles, suchas silica particles, dispersed in a fluid. Measurement of zeta potentialcan have a variance of, for instance +/−2 mV, and, as used herein, zetapotential magnitude refers to the absolute value of the number, e.g., azeta potential value of minus 30 mV has a greater magnitude than a zetapotential value of minus 10 mV.

As used herein, “destabilized dispersion” means a suspension of solidparticles in an aqueous fluid wherein the charge at the surface of theparticles has been reduced by the presence of an agent, or by treatmentof the solid particles, and is characterized by a zeta potentialmagnitude of less than 30 mV, or more preferably a zeta potential ofless than 28 mV or less than 25 mV. The aqueous fluid can be water, awater miscible fluid (e.g., alcohol or ether), partially water misciblefluid, or a mixture of fluids that contains at least a water miscible orpartially water miscible fluid.

As used herein, the terms “silica slurry” and “dispersion” mean adispersion of silica in an aqueous fluid, wherein the charge at thesurface of the silica prevents particle agglomeration and the dispersionis characterized by a zeta potential value with a magnitude of at least30 mV. A silica slurry or dispersion may be destabilized by treatmentwith sufficient agent(s), or by treatment of the silica, to reduce thecharge on the surface of the silica and the resulting destabilizedsilica slurry (or destabilized silica dispersion) is characterized by azeta potential magnitude of less than 30 mV.

As used herein, the terms “uniform”and “uniformly” are intended to mean,conventionally for those skilled in the art, that the concentration of acomponent, for example, particulate tiller, in any given fraction orpercentage (e.g., 5%) of a volume is the same (e.g., within 2%) as theconcentration of that component in the total volume of the material inquestion, e.g., elastomer composite or dispersion. Those skilled in theart will be able to verify the statistical uniformity of the material,if required, by means of measurements of concentration of the componentusing several samples taken from various locations (for example near thesurface or deeper in the bulk).

As used herein, a “silica elastomer composite” means a masterbatch (apremixture of reinforcing material, elastomer, and various optionaladditives, such as extender oil) of coherent rubber comprising areinforcing amount (e.g., about 15 phr to about 180 phr) of dispersedsilica. Silica elastomer composite can contain optional, furthercomponents such as acid, salt, antioxidant, antidegradants, couplingagents, minor amounts (e.g., 10 wt % or less of total particulates) ofother particulates, processing aids, and/or extender oil, or anycombinations thereof.

As used herein, a “solid silica-containing continuous rubber phase”means a composite having a continuous rubber phase and a uniformlydispersed phase of silica and, for instance, up to 90%, by weight,aqueous fluid. The solid silica-containing continuous rubber phase maybe in the form of a continuous rope or worm. When compressed thesearticles release water. The solid silica-containing continuous rubberphase can contain optional, further components such as acid, salt,antioxidant, coupling agents, minor amounts of other particulates (e.g.,10 wt % or less of total particulates), and/or processing oil, or anycombinations thereof.

As used herein, a “semi-solid silica-containing continuous rubber phase”means a composite with a paste-like consistency, having asilica-containing, continuous rubber phase. The semi-solid product has acontinuous phase of rubber, with entrapped silica uniformly distributedthroughout the rubber phase. The semi-solid silica-containing continuousrubber phase remains coherent and expels water, while retaining solidscontent, upon further handling in one or more subsequent operationsselected to develop the paste-like or gel-like material into a solidsilica-containing continuous rubber phase.

As used herein, a “coherent” material is material existing in asubstantially unitary form that has been created by the adhesion of manysmaller parts, such as an elastic, solid mass of rubber created by theadhesion of many small rubber particles to each other.

As used herein, a “continuous flow” is a steady or constant flow of afluid without interruption from a supply source (e.g., tank). But, it isto be understood that temporary interruptions (e.g., a second or a fewminutes) of flow would still be considered a continuous flow (e.g., forinstance, when switching supply from various supply holding areas, suchas tanks and the like, or interrupting flows to accommodate downstreamunit processes or maintenance of the equipment).

The elastomer composite can be produced in a continuous flow processinvolving a liquid mixture of elastomer latex and destabilizeddispersion of silica. Any device, or apparatus or system can be used,provided the device, apparatus, or system can be operated such that aliquid mixture of elastomer latex and a destabilized silica dispersioncan be combined under continuous flow conditions and under controlledvolumetric flow, pressure, and velocity conditions, including, but notlimited to, the apparatus shown in FIG. 1A, 1B, or 1C, or any type ofeductor or ejector, or any other device arranged to combine a continuousflow of at least two flows of liquid under controlled volumetric flow,pressure, and velocity conditions into and through a reaction zone. Theapparatus described in U.S.20110021664, U.S. Pat. No. 6,048,923,WO2011034589, WO2011034587, U.S.20140316058, and WO2014110499 (eachincorporated in their entirety by reference) can be used or adapted tothe processes herein as well. Also, ejectors and eductors or syphonssuch as water jet eductors or steam jet syphons can be used (e.g, onescommercially available from Schutte & Koerting, Trevose, Pa.).

The apparatus can include various supply tanks, pipes, valves, metersand pumps to control volumetric flow, pressure, and velocity. Further,as indicated at inlet (3) in FIGS. 1A, 1B, and 1C, various types andsizes of nozzles or other orifice size control elements (3 a) can beemployed to control the velocity of the silica slurry. The volumetricdimension of the reaction zone (13) can be selected to provide desiredvolumetric flows of the fluids and the elastomer composite. The inlet(11) supplying the elastomer latex to the reaction zone may be taperedto provide different volumetric flow rates and velocities. Devices mayinclude an inlet (11) of uniform diameter, without any taper at theorifice leading to the reaction zone.

In the method, a fluid that includes an elastomer latex and anadditional fluid that includes a destabilized dispersion of silicasupplied, for instance, as a jet under pressure are combined togetherunder continuous flow conditions and under selected volumetric flowrates, pressure, and velocities to rapidly and intimately mix the twofluids. The combining, for instance in a semi-confined space underpressure, is such that the silica is distributed throughout theelastomer latex and, in parallel, the elastomer latex is transformedfrom a liquid to a solid or semi-solid phase, i.e., a liquid to solidinversion, or coagulation, of the latex occurs, capturing thedistributed silica and water in the rubber and forming a solid orsemi-solid silica-containing continuous rubber phase in a continuous orsemi-continuous flow out of the reaction zone (e.g., from opening atoutlet (7) in FIGS. 1A-1C). At this point, the product can be consideredan elastomer composite of a continuous rubber phase containing silicaparticles, a silica-containing coherent rubber, or a silica elastomercomposite. It is believed that the silica particles first must bedistributed in the elastomer latex to obtain the desired product, andthe liquid to solid phase inversion follows immediately upon the silicadistribution. However, with the continuous and extremely rapid rate ofcombining the fluids (i.e., less than 2 seconds, less than 1 second,less than 0.5 second, less than 0.25 second, less than 0.1 second, or onthe order of milliseconds), and the energetic and intimate mixing ofrelatively small volumes of fluids in the reaction zone (e.g., fluidvolumes on the order of 10 to 500 cc), the parallel steps ofdistribution of the silica particles and liquid to solid phasetransformation of the elastomer latex can happen nearly simultaneously.The ‘reaction zone’ as used herein is the zone where the intimate mixingoccurs along with coagulation of the mixture. The mixture moves throughthe reaction zone and to outlet (7).

An exemplary method for preparing the elastomer composite involvessimultaneously feeding a first fluid comprising a destabilizeddispersion of silica and a second fluid comprising an elastomer latex(e.g. natural rubber latex) fluid to a reaction zone. The first fluidcomprising the destabilized dispersion of silica can be fed at a flowrate based on its volume, and the second fluid comprising the elastomerlatex can be fed at a flow rate based on its volume (i.e., volumetricflow rates). The volumetric flows of either the first fluid, the secondfluid, or both the first and second fluid can be adjusted or provided soas to yield an elastomer composite having a silica content of from 15 to180 parts per hundred weight rubber (phr) (e.g., from 35 to 180 phr,from 20 phr to 150 phr, from 25 phr to 125 phr, from 25 phr to 100 phr,from 35 to 115 phr, or from 40 phr to 115 phr, or from 40 phr to 90 phrand the like). The fluid that contains the destabilized dispersion ofsilica may be referred to as the first fluid in some embodiments herein.This fluid is a separate fluid from the fluid containing the elastomerlatex. Either fluid can be introduced through one inlet or injectionpoint or through more than one inlet or injection point.

The volumetric flow ratio of the first fluid (destabilized silicadispersion) to the second fluid (latex fluid) can be adjusted to permitthe desired elastomer composite to form. Examples of such volumetricflow ratios include, but are not limited to, a volumetric ratio of from0.4:1 (first fluid to second fluid) to 3.2:1; from 0.2:1 to 2:1 and thelike. The volumetric flow ratio between the first fluid and second fluidcan be adjusted by any means or technique. For instance, the volumetricflow rate of the first or second fluid or both can be adjusted by a)increasing the volumetric flow rate, b) decreasing the volumetric flowrate, and/or c) adjusting the flow rates of the fluids relative to eachother. Pressure created by physical constraints applied to the flow ofthe first fluid causes formation of a high velocity jet that enables thecombination of the destabilized silica dispersion with the elastomerlatex to occur rapidly, e.g., in a fraction of a second. As an example,the time during which two fluids are mixed and a liquid to solid phaseinversion occurs can be on the order of milliseconds (e.g., about 50 msto about 1500 ms or about 100 ms to about 1000 ms). For a givenselection of fluids, if the velocity of the first fluid is too slow toadequately mix the fluids, or the residence time is too short, then asolid rubber phase and solid product flow may not develop. If theduration of the process is too long, back pressure may develop in thereaction zone and the continuous flow of materials halted. Likewise, ifthe velocity of the first fluid is too fast, and the duration of theprocess is too short, a solid rubber phase and solid product flow maynot develop.

As described earlier, the relative volumetric flows of the first fluid(destabilized silica slurry) and the second fluid (latex) can beadjusted, and when at least one salt is used as the destabilizationagent, it is preferred to adjust the volumetric flow ratio ofdestabilized silica slurry to elastomer latex so as to be 0.4:1 to3.2:1. Other flow ratios may be used.

When at least one acid is used as the destabilization agent, it ispreferred to adjust the volumetric flow ratio of destabilized silicaslurry to elastomer latex so as to be 0.2:1 to 2:1. Other flow ratiosmay be used.

The elastomer latex can contain at least one base (such as ammonia), andthe destabilized dispersion of silica can be achieved with the additionof at least one acid, wherein the molar ratio of the acid in the firstfluid (silica) and the base (e.g., ammonia) in the second fluid (latex)is at least 1.0, or at least 1.1, or at least 1.2, such as from 1 to 2or 1.5 to 4.5. The base can be present in a variety of amounts in theelastomer latex, such as, but not limited to, 0.3 wt% to about 0.7 wt%(based on the total weight of the elastomer latex), or other amountsbelow or above this range.

The destabilized silica dispersion can be fed to the reaction zonepreferably as a continuous, high velocity, e.g., about 6 m/s to about250 m/s, or about 30 m/s to about 200 m/s, or about 10 m/s to about 150m/s, or about 6 m/s to about 200 m/s, jet of injected fluid, and thefluid containing the elastomer latex can be fed at a relatively lowervelocity, e.g., about 0.4 m/s to about 11 m/s, or about 0.4 m/s to about5 m/s, or about 1.9 m/s to about 11 m/s, or about 1 m/s to about 10 m/sor about 1 m/s to about 5 m/s. The velocities of the fluids are chosenfor optimizing mixing between fluids and fast coagulation of elastomerlatex. The velocity of the elastomer latex fed into the reaction zoneshould be preferably high enough to generate turbulent flow for bettermixing with destabilized silica slurry. Yet, the velocity of theelastomer latex should be kept low enough so that latex would notcoagulate from shear before it is well mixed with the destabilizedsilica slurry. In addition, the velocity of the elastomer latex shouldbe kept low enough before it enters into the reaction zone forpreventing clogging of latex supply lines from coagulation of latex dueto high shear. Similarly, there is also an optimized range of thevelocity of destabilized silica dispersion . It is theorized that if thevelocity of the destabilized silica slurry is too high, the rate ofshear induced agglomeration of silica particles could be too high toallow adequate, uniform mixing between silica particles and elastomerlatex particles.

Shear thickening from agglomeration and networking of silica particlesalso could reduce turbulence of the destabilized silica slurry andadversely affect the mixing between silica and latex. On the other hand,if the velocity of the destabilized silica slurry is too low, there maynot be sufficient mixing between silica particles and elastomer latexparticles. Preferably, at least one of the fluids entering into thereaction zone has a turbulent flow. In general, due to much higherviscosity of a typical destabilized silica dispersion relative to atypical elastomer latex, a much higher velocity of the destabilizedsilica dispersion is needed for generating good fluid dynamics formixing with the elastomer latex and fast coagulation of the latex. Suchhigh velocity flow of the destabilized silica dispersion may inducecavitation in the reaction zone to enhance rapid mixing of fluids anddistribution of silica particles in the elastomer latex. The velocity ofthe destabilized silica dispersion can be altered by using differentvolumetric flow rates, or a different nozzle or tip (3 a) (wider ornarrower in diameter) at the inlet (3) that feeds the first fluidcomprising destabilized silica dispersion. With use of a nozzle toincrease the velocity of the destabilized silica dispersion, it can beprovided under pressure ranging from about 30 psi to about 3,000 psi, orabout 30 psi to about 200 psi, or about 200 psi to about 3,000 psi, orabout 500 psi to about 2,000 psi or a relative pressure at least 2 timeshigher than the pressure applied to the fluid containing the elastomerlatex, or 2 to 100 times higher. The second fluid of elastomer latex canbe provided, as an example, at a pressure ranging from about 20 psi toabout 30 psi. The pressure in the first fluid supply system may be up toabout 500 psi.

Based on the production variables described herein, such as the velocityof the destabilized silica slurry fluid, the velocity of the latexfluid, the relative flow rates of the destabilized silica slurry andlatex fluids, the concentration of the destabilizing agent such as asalt and/or acid, the silica concentration in the destabilized slurry,the rubber weight percent in the latex, the ammonia concentration in thelatex, and/or the acid (if present) to ammonia ratio, it is possible tocontrol, obtain, and/or predict formation of a solid or semi-solidsilica-containing continuous rubber phase over a range of desired silicacontents. Thus, the process can be operated over an optimized range ofvariables. Thus, the a) velocity of one or both fluids, b) thevolumetric flow ratio of the fluids, c) the destabilized nature of thesilica, d) particulate silica concentration, e.g., 6 to 35 weightpercent, of the destabilized silica dispersion, and e) the dry rubbercontent, e.g., 10 to 70 weight percent, of the latex, can permit mixingunder high impact conditions so as to cause a liquid to solid inversionof the elastomer latex and uniformly disperse the silica in the latex ata selected silica to rubber ratio, and thus form a flow of a solid orsemi-solid silica-containing continuous rubber phase. The recovery ofthe flow of solid or semi-solid silica-containing continuous rubberphase can be achieved in any conventional technique for recovery of asolid or semi-solid flow of material. The recovery can permit the solidor semi-solid flow to enter into a container or tank or other holdingdevice. Such container or holding tank may contain a solution of salt oracid or both to effect further coagulation of the product to a moreelastic state. For example, the recovering can be transporting orpumping the solid flow to other processing areas or devices for furtherprocessing, of which some options are described herein. The recoveringcan be continuous, semi-continuous, or by batch. The outflow end of thereaction zone preferably is semi-confined and open to the atmosphere,and the flow of solid or semi-solid elastomer composite is preferablyrecovered at ambient pressure to allow continuous operation of theprocess.

The flow of a solid silica-containing continuous rubber phase can be inthe form of more or less elastic, rope-like “worms” or globules. Thesolid silica-containing continuous rubber phase may be capable of beingstretched to 130-150% of its original length without breaking. In othercases, a semi-solid silica-containing continuous rubber phase can be inthe form of non-elastic, viscous paste or gel-like material that candevelop elastic properties. In each case, the output is a coherent,flowing solid whose consistency can be highly elastic or slightlyelastic and viscous. The output from the reaction zone can be asubstantially constant flow concurrent with the on-going feeding of theelastomer latex and the destabilized dispersion of silica fluids intothe reaction zone. Steps in the process, such as the preparation of thefluids, may be done as continuous, semi-continuous, or batch operations.The resulting solid or semi-solid silica-containing continuous rubberphase can be subjected to subsequent further processing steps, includingcontinuous, semi-continuous, or batch operations.

The solid or semi-solid silica-containing continuous rubber phasecreated in the process contains water, or other aqueous fluid, andsolutes from the original fluids, and, for instance, can contain fromabout 40 wt % to about 95 wt % water, or 40 wt % to about 90 wt % water,or from about 45 wt % to about 90 wt % water, or from about 50 to about85 wt % water content, or from about 60 to about 80 wt % water, based onthe total weight of the flow of silica elastomer composite. As anoption, after forming the solid or semi-solid silica-containing rubberphase comprising such water contents, this product can be subjected tosuitable de-watering and masticating steps and compounding steps todevelop desired rubber properties and fabricate rubber compounds.Further details of the process and other post-processing steps are setforth below and can be used in any embodiment of the present invention.

A semi-solid silica-containing continuous rubber phase may be convertedto a solid silica-containing continuous rubber phase. This for instancecan be done by subjecting the semi-solid silica-containing continuousrubber phase to mechanical steps that remove water from the compositeand/or having the semi-solid material sit for a time (e.g., afterrecovery from the reaction zone in an offline location) for instance, 10minutes to 24 hours or more; and/or heating the semi-solidsilica-containing continuous rubber phase to remove water content (e.g.,a temperature of from about 50 ° C. to about 200 ° C.); and/orsubjecting the semi-solid material to acid or additional acid such as inan acid bath, or to salt or additional salt, or a salt bath, or to acombination of acid and salt, and the like. One or more or all of thesesteps can be used. In fact, one or more or all of steps can be used as afurther processing step(s) even when a solid silica-containingcontinuous rubber phase is initially or subsequently recovered.

The degree of destabilization of the silica slurry, at least in part,determines the amount of silica that can be present in the silicaelastomer composite (e.g., captured and distributed uniformly within thecomposite) for a given silica concentration in the silica slurry and agiven dry rubber content of the latex. At lower selected target silicato rubber ratios (e.g., 15 phr to 45 phr), the concentration ofdestabilizing agent may not be high enough in the silica slurry andultimately the silica/latex mixture to rapidly coagulate and form asolid or semi-solid silica-containing continuous rubber phase. Inaddition, selecting appropriate silica and rubber concentrations andappropriate relative fluid flow rates as described herein areconsiderations for forming the solid or semi-solid product. For example,at relatively low volumetric flow ratios of destabilized slurry tolatex, the amount of the destabilizing agent in the destabilized silicaslurry may not be sufficient to facilitate rapid coagulation ofelastomer latex in the reaction zone. Generally, for a given elastomerlatex, lower silica loadings can be achieved by increasing thedestabilization of the silica slurry and/or reducing the weightpercentage of silica in the destabilized slurry.

When a dispersion of silica is destabilized, the silica particles tendto flocculate. When a dispersion of silica is too highly destabilized,the silica can ‘fall out’ of solution and become unsuited for use inpreferred embodiments.

When destabilization occurs, the surface charges on the silica aretypically not completely removed. However, sometimes when the silicaparticle, or the silica dispersion, is treated to destabilize, theisoelectric point (IEP) may be crossed over from a negative zetapotential to a positive zeta potential value. Generally for silica, thenet charge on the surface of the silica particles is reduced and themagnitude of the zeta potential is decreased during destabilization.

For higher silica to rubber ratios in the silica elastomer composite,one may select higher silica concentrations in the destabilized slurryand/or a higher silica fluid to latex fluid volumetric flow ratio. Oncethe silica slurry is destabilized and initially combined with the latexfluid, if the mixture does not coagulate, the volume flow ratio of thefirst fluid and second fluid can be adjusted, such as by decreasing thevolume flow of latex, which effectively provides a higher silica torubber ratio in the elastomer composite. In this step of adjusting theamount of latex present, the amount of latex is, or becomes, an amountthat does not cause excessive dilution of the concentration of thedestabilizing agent in the overall mixture such that the desired productcan be formed within the residence time in the reaction zone. To obtaina desired silica to rubber ratio in the elastomer composite, variousoptions are available. As an option, the level of destabilization of thesilica slurry can be increased, such as by reducing the magnitude of thezeta potential of the destabilized silica slurry (e.g., by adding moresalt and/or acid). Or, as an option, the silica concentration in thedestabilized silica slurry can be adjusted, for instance, by lowering orincreasing the silica concentration in the destabilized silica slurry.Or, as an option, a latex can be used that has a higher rubber content,or a latex can be diluted to a lower rubber content, or the relativeflow rate of the latex can be increased. Or, as an option, the flow rateand orifice size (where each can control or affect velocity of thefluid(s)) or relative orientation of the two fluid flows can be modifiedto shorten or lengthen the residence time of the combined fluids in thereaction zone, and/or alter the amount and type of turbulence at thepoint of impact of the first fluid on the second fluid. Any one or twoor more of these options can be used to adjust the process parametersand obtain a target or desired silica to rubber ratio in the elastomercomposite.

The amount or level of destabilization of the silica slurry is a majorfactor in determining what silica to rubber ratio can be achieved in thesilica elastomer composite. A destabilizing agent used to destabilizesilica in the slurry may play a role in accelerating coagulation ofelastomer latex particles when the destabilized silica slurry is mixedwith elastomer latex in the reaction zone. It is theorized that the rateof latex coagulation in the reaction zone may depend on theconcentration of the destabilizing agent in the combined fluids. It hasbeen observed that by running the process for producing silica elastomercomposite under various conditions, one may determine a thresholdconcentration of a destabilizing agent present in the combined mixtureof fluids at the time of mixing that is effective to produce solid orsemi-solid silica-containing continuous rubber phase. An example ofselecting and adjusting process conditions to achieve the thresholdconcentration to yield solid or semi-solid silica-containing continuousrubber phase, is described in the Examples below. If the thresholdconcentration for a given selection and composition of fluids,volumetric flows, and velocities is not equaled or exceeded, a solid orsemi-solid silica-containing continuous rubber phase will generally notbe produced.

The minimum amount of destabilization of the silica slurry is indicatedby a zeta potential magnitude of less than 30 mV (e.g. with zetapotentials such as −29.9 mV to about 29.9 mV, about −28 mV to about 20mV, about −27 mV to about 10 mV, about −27 mV to about 0 mV, about −25mV to about 0 mV, about −20 mV to about 0 mV, about −15 mV to about 0mV, about −10 mV to about 0 mV and the like). If the silica slurry hasbeen destabilized to within this zeta potential range, then the silicain the destabilized slurry can be incorporated into a solid orsemi-solid silica-containing continuous rubber phase when combined withthe elastomer latex.

While it may be desirable to destabilize the latex before combining itwith the silica slurry, under shear conditions such as those presentwhile continuously pumping the latex into the reaction zone, it isdifficult to destabilize the latex fluid beforehand without causingpremature coagulation of the latex. However, the destabilization agentused in the destabilized silica slurry may be present in a surplusamount to enhance destabilization of the latex, and/or mitigate dilutionof the agent once the destabilized silica slurry and latex fluid arecombined. As a further option, at especially high silica concentrations(e.g., >25 wt % silica in the silica slurry), some added destabilizationagent can be added separately to the mixture of the destabilized silicaslurry and elastomer latex in the reaction zone to enhance coagulationof the latex.

Without wishing to be bound to any theory, the process for producingsilica elastomer composite is believed to form interpenetrated coherentnetworks of both rubber particles and silica aggregates in about twoseconds or less, such as a fraction of a second, as the two fluidscombine and the phase inversion occurs, resulting in a solid orsemi-solid material comprising these networks with encapsulated water.Such fast network formation allows the continuous production of a solidor semi-solid silica-containing continuous rubber phase. It is theorizedthat shear induced agglomeration of silica particles as the destabilizedsilica slurry passes through an inlet nozzle to be combined with theelastomer latex may be useful for creating unique, uniform particlearrangement in rubber masterbatches and capturing silica particleswithin rubber through hetero-coagulation between silica and rubberparticles. It is further theorized that without such an interpenetratednetwork, there may not be a composite of a solid or semi-sold,continuous rubber phase containing dispersed silica particles, in theshape of a worm, or solid pieces, for instance, that encapsulates 40-95wt % water and retains all or most of the silica in subsequentdewatering processes including squeezing and high energy mechanicalworking.

It is theorized that the formation of a silica network arises, at leastin part, from shear induced silica particle agglomeration as thedestabilized silica slurry passes through a pressurized nozzle (3 a) athigh velocity through the first inlet (3) into the reaction zone (13),as shown in FIGS. 1A-1C. This process is facilitated by reduction ofstability of silica in the destabilized slurry when the silica slurryhas been destabilized (e.g., by treating the silica slurry with salt oracid or both).

It is theorized that the liquid to solid phase inversion of the latexmay result from various factors, including shear induced coagulationfrom mixing with the high velocity jet of destabilized silica slurry,interaction of the silica surface with the latex components, ionic orchemical coagulation from contact with the silica slurry containingdestabilizing agent, and a combination of these factors. In order toform composite material comprising the interpenetrated silica networkand rubber network, the rates of each network formation as well as therate of mixing should be balanced. For example, for highly destabilizedsilica slurries at a high salt concentration in the slurry,agglomeration and network formation of silica particles occurs rapidlyunder shear conditions. In this case, volumetric flows and velocitiesare set so the latex has a rapid rate of coagulation for formation ofthe interpenetrated silica/rubber networks. Rates of formation areslower with more lightly destabilized silica slurries.

One exemplary process to produce a silica elastomer composite includesfeeding a continuous flow of a fluid that contains at least elastomerlatex (sometimes referred to as the second fluid) through inlet 11(FIGS. 1A, 1B, and/or 1C), to a reaction zone 13 at a volumetric flowrate of about 20 L/hr to about 1900 L/hr. The method further includesfeeding a continuous flow of a further fluid containing a destabilizeddispersion of silica through inlet 3 (sometimes referred to as the firstfluid) under pressure that can be accomplished by way of nozzle tips (inFIGS. 1A-1C, at 3 a) at a volumetric flow rate of 30 L/hr to 1700 L/hr.The destabilized state of the silica dispersion and the impacting of thetwo fluid flows (introduced at inlets 3 and 11) under high energyconditions created by introducing the first fluid as a high velocity jet(e.g., about 6 m/s to about 250 m/s) that impacts the lower velocitylatex flow (e.g., 0.4-11 m/s) entering the reaction zone at an angleapproximately perpendicular to the high speed jet of the first fluid iseffective to intimately mix the silica with the latex flow, promoting auniform distribution of silica in the flow of solid silica-containingcontinuous rubber phase from the outlet of the reaction zone.

As an option, the elastomer latex introduced, for instance, throughinlet 11 can be a blend of two or more latexes, such as a blend of twoor more synthetic latexes. As an option, the devices in FIGS. 1A, 1B,and/or 1C can be modified to have one or more additional inlets so as tointroduce other components to the reaction zone, such as one or moreadditional latexes. For instance, in FIG. 1C, inlet 14 can be used tointroduce a further latex besides using inlet 11. The one or moreadditional inlets can be sequential to each other, or be adjacent toeach other or set forth in any orientation as long as the material (e.g.latex) being introduced through the inlet(s) has sufficient time todisperse or be incorporated into the resulting flow. In WO 2011/034587,incorporated in its entirety by reference herein, FIGS. 1, 2A, and 2Bprovide examples of additional inlets and their orientations which canbe adopted here for use with embodiments of the present invention. As aparticular example, one inlet can introduce a flow that includes naturalrubber latex and an additional inlet can introduce a synthetic elastomerlatex, and these latex flows are combined with the flow of thedestabilized dispersion of silica to result in the flow of a solid orsemi-solid silica-containing continuous rubber phase. When more than oneinlet is utilized for elastomer latex introduction, the flow rates canbe the same or different from each other.

FIG. 2 sets forth an example, using a block diagram of various stepsthat can occur in the formation of the elastomer composite. As shown inFIG. 2, the destabilized dispersion of silica (first fluid) 100 isintroduced into the reaction zone 103 and the fluid containing theelastomer latex (second fluid) 105 is introduced also into the reactionzone 103. As an option, a flow of solid or semi-solid silica-containingcontinuous rubber phase exits the reaction zone 103 and can optionallyenter a holding zone 116 (e.g., a holding tank, with or without theaddition of a salt or acid solution to further enhance coagulation ofrubber and formation of silica/rubber networks); and can optionallyenter, directly, or after diversion to a holding zone 116, a dewateringzone 105; can optionally enter a continuous mixer/compounder 107; canoptionally enter a mill (e.g., open mill, also called a roll mill) 109;can be subjected to additional extra milling 111 (same or differentconditions as mill 109) (such as same or different energy input); can besubjected to optional mixing by mixer 115, and/or can be granulatedusing a granulator 117, and then can optionally be baled, using a baler119, and can optionally be broken down by use of an additional mixer121.

With regard to the silica, one or more types of silica, or anycombination of silica(s), can be used in any embodiment of the presentinvention. The silica suitable for reinforcing elastomer composites canbe characterized by a surface area (BET) of about 20 m²/g to about 450m²/g; about 30 m²/g to about 450 m²/g; about 30 m²/g to about 400 m²/g;or about 60 m²/g to about 250 m²/g; and for heavy vehicle tire treads aBET surface area of about 60 m²/g to about 250 m²/g or for example fromabout 80 m²/g to about 200 m²/g. Highly dispersible precipitated silicacan be used as the filler in the present methods. Highly dispersibleprecipitated silica (“HDS”) is understood to mean any silica having asubstantial ability to dis-agglomerate and disperse in an elastomericmatrix. Such determinations may be observed in known manner by electronor optical microscopy on thin sections of elastomer composite. Examplesof commercial grades of HDS include, Perkasil® GT 3000GRAN silica fromWR Grace & Co, Ultrasil® 7000 silica from Evonik Industries, Zeosil®1165 MP and 1115 MP silica from Solvay S.A., Hi-Sil® EZ 160G silica fromPPG Industries, Inc., and Zeopol® 8741 or 8745 silica from JM HuberCorporation. Conventional non-HDS precipitated silica may be used aswell. Examples of commercial grades of conventional precipitated silicainclude, Perkasil® KS 408 silica from WR Grace & Co, Zeosil® 175GRsilica from Solvay S.A., Ultrasil® VN3 silica from Evonik Industries,Hi-Sil® 243 silica from PPG Industries, Inc. and the Hubersil® 161silica from JM Huber Corporation. Hydrophobic precipitated silica withsurface attached silane coupling agents may also be used. Examples ofcommercial grades of hydrophobic precipitated silica include Agilon®400,454, or 458 silica from PPG Industries, Inc. and Coupsil silicas fromEvonik Industries, for example Coupsil 6109 silica.

Typically the silica (e.g., silica particles) have a silica content ofat least 20 wt %, at least 25 wt %, at least 30 wt %, at least 35 wt %,at least 40 wt %, at least 50 wt %, at least 60 wt %, at least 70 wt %,at least 80 wt %, at least 90 wt %, or almost 100 wt % or 100 wt %, orfrom about 20 wt % to about 100 wt %, all based on the total weight ofthe particle. Any of the silica(s) can be chemically functionalized,such as to have attached or adsorbed chemical groups, such as attachedor adsorbed organic groups. Any combination of silica(s) can be used.The silica that forms the silica slurry and/or destabilized silicaslurry can be in part or entirely a silica having a hydrophobic surface,which can be a silica that is hydrophobic or a silica that becomeshydrophobic by rendering the surface of the silica hydrophobic bytreatment (e.g., chemical treatment). The hydrophobic surface may beobtained by chemically modifying the silica particle with hydrophobizingsilanes without ionic groups, e.g.,bis-triethoxysilylpropyltetrasulfide. Such a surface reaction on silicamay be carried out in a separate process step before dispersion, orperformed in-situ in a silica dispersion. The surface reaction reducessilanol density on the silica surface, thus reducing ionic chargedensity of the silica particle in the slurry. Suitable hydrophobicsurface-treated silica particles for use in dispersions may be obtainedfrom commercial sources, such as Agilon® 454 silica and Agilon® 400silica, from PPG Industries. Silica dispersions and destabilized silicadispersions may be made using silica particles having low surfacesilanol density. Such silica may be obtained through dehydroxylation attemperatures over 150° C. via, for example, a calcination process.

Further, the silica slurry and/or destabilized silica slurry cancontain, as an option, a minor amount (10 wt % or less, based on a totalweight of particulate material) of any non-silica particles, such ascarbon black(s) or zinc oxide, or calcium carbonate, or otherparticulate materials useful in rubber compositions (e.g., 95 wt %precipitated silica and 5 wt % carbon black). Any reinforcing ornon-reinforcing grade of carbon black may be selected to yield thedesired property in the final rubber composition.

Silica may be dispersed in aqueous fluid according to any techniqueknown to those of skill in the art. A dispersion of particulate silicacan be subjected to mechanical processing, for instance, to reduceparticle size. This can be done prior to or during or afterdestabilizing of the dispersion and can contribute in a minor way ormajor way to the destabilizing of the dispersion. The mechanicalprocessing can comprise or include grinding, milling, comminution,bashing, or high shear fluid processing, or any combinations thereof.

For example, a silica slurry can be made by dispersing silica in a fluidby means of a grinding process. Such a grinding process reduces the sizeof most silica agglomerates (e.g. over 80% by volume) in the fluid tobelow 10 microns, and preferably below 1 micron, the typical size rangeof colloidal particles. The fluid may be water, an aqueous fluid, or anon-aqueous polar fluid. The slurry, for instance, may comprise fromabout 6 wt % to about 35 wt % silica-containing particles, based on theweight of the slurry. The size of silica particles may be determinedusing a light scattering technique. Such a slurry when made in waterusing silica particles having low residual salt content at a pH of 6-8,typically has a zeta potential magnitude higher than, or equal to, 30 mVand shows good stability against aggregation, gelling, and settlement ina storage tank with slow stirring (e.g. stirring speed below 60 RPM). Aswell-ground silica particles are generally stable in water at a pH ofaround 7 due to high negative charges on silica, very high shear isgenerally needed to overcome the repulsive energy barrier betweenparticles to induce particle agglomeration.

In an exemplary method employing silica, such as HDS granules, thesilica can be combined with water, and the resulting mixture is passedthrough a colloid mill, pipeline grinder, or the like to form adispersion fluid. This fluid is then passed to a homogenizer that morefinely disperses the filler in the carrier liquid to form the slurry.Exemplary homogenizers include, but are not limited to, theMicrofluidizer® system commercially available from MicrofluidicsInternational Corporation (Newton, Mass., USA). Also suitable arehomogenizers such as models MS18, MS45 and MC120, and serieshomogenizers available from the APV Homogenizer Division of APV Gaulin,Inc. (Wilmington, Mass., USA). Other suitable homogenizers arecommercially available and will be apparent to those skilled in the artgiven the benefit of the present disclosure. The optimal operatingpressure across a homogenizer may depend on the actual apparatus, thesilica type, and/or the silica content. As an example, a homogenizer maybe operated at a pressure of from about 10 psi to about 5000 psi orhigher, for example, from about 10 psi to about 1000 psi, about 1000 psito about 1700 psi, about 1700 psi to about 2200 psi, about 2200 psi toabout 2700 psi, about 2700 psi to about 3300 psi, about 3300 psi toabout 3800 psi, about 3800 psi to about 4300 psi, or about 4300 psi toabout 5000 psi. As indicated earlier, the dispersion of particulatesilica is destabilized before carrying out the masterbatch process, andthe dispersion can be destabilized by following one of the techniquesmentioned herein, before, during, or after any grinding or similarmechanical process.

Depending on the wet masterbatch method employed, a high silicaconcentration in slurry may be used to reduce the task of removingexcess water or other carrier. For the destabilized dispersion of silicaparticles, the liquid used can be water or other aqueous fluid or otherfluid. For the destabilized dispersion, from about 6 weight percent toabout 35 weight percent filler may be employed, for example, from about6 weight percent to about 9 weight percent, from about 9 weight percentto about 12 weight percent, from about 12 weight percent to about 16weight percent, from about 10 weight percent to about 28 weight percent,from about 16 weight percent to about 20 weight percent, from about 20weight percent to about 24 weight percent, from about 24 weight percentto about 28 weight percent, or from about 28 weight percent to about 30weight percent, based on the weight of the destabilized dispersion. Forthe destabilized dispersion, a higher silica concentration can havebenefits. For instance, silica concentration in the destabilized slurrycan be at least 10 weight percent or at least 15 weight percent, basedon the weight of the slurry (e.g., about 12 wt % to about 35 wt % orabout 15.1 wt % to about 35 wt %, or about 20 wt % to about 35 wt %),which can provide benefits such as, but not limited to, reducedwastewater, increased production rates, and/or reduction of theequipment size needed for the process. Those skilled in the art willrecognize, given the benefit of this disclosure, that the silicaconcentration (in weight percent) of the silica slurry (and in thedestabilized silica slurry) should be coordinated with other processvariables during the wet process to achieve a desired silica to rubberratio (in phr) in the ultimate product.

Details of a dispersion of silica are further described below. Ingeneral, a dispersion can be a material comprising more than one phasewhere at least one of the phases contains or includes or consists offinely divided phase domains, optionally in the colloidal size range,dispersed throughout a continuous phase. A dispersion or slurry ofsilica or silica dispersion can be prepared as a stable suspension ofparticulate silica in aqueous fluid, wherein the charge at the surfaceof the particles prevents particle agglomeration and the dispersion ischaracterized by a zeta potential magnitude of greater than or equal to30 mV. In such dispersions, the silica particles remain in stabledispersion, and/or suspension, with respect to aggregation andcoalescence, for instance, for at least 8 hours. A stable dispersion canbe one where constant particle size is maintained, and wherein theparticles do not settle or gel, or take a very long time to settleappreciably in the presence of slow or periodic stirring, for example,not settling appreciably after 8 hours, or 12 hours or 24 hours, or 48hours. For instance, for colloidal silica particles well dispersed inaqueous fluid, stability can generally be observed from a pH of 8 to 10.Further, with slow stirring of the dispersion, the silica particlesremain suspended in the fluid by means of particle surface charge,particle surface polarity, pH, selected particle concentration, particlesurface treatment, and combinations thereof. The fluid may be or includewater, an aqueous mixture, or a water miscible or partially misciblefluid, such as various alcohols, ethers, and other low molecular weightwater-miscible solvents, preferably having C₁-C₅ organic groups (e.g.,ethanol, methanol, propanol, ethyl ether, acetone, and the like). Asindicated above, the dispersion, for instance, may comprise about 6 wt %to about 35 wt %, about 10 wt % to about 28 wt %, about 12 wt % to about25 wt %, or about 15 wt % to about 30 wt % silica-containing particles,based on the weight of the dispersion.

A stable dispersion may be a colloidal dispersion. In general, acolloidal dispersion or colloid can be a substance where dispersedparticles are suspended throughout another substance. Thedispersed-phase particles have a diameter of from approximately about 1nanometer to about 1000 nanometers, and typically about 100 nanometersto about 500 nanometers. In a stable colloidal dispersion, particlesize, density, and concentration are such that gravity does not causeparticles to settle out of dispersion easily. Colloids with themagnitude of zeta potential of 30 mV or over are generally regarded asstable colloidal systems. Reduction of particle stability (e.g., silica)in a colloid or dispersion due to charge stabilization can be measuredby reduction of magnitude of zeta potential. Particle size may bemeasured by a light scattering method.

A destabilized silica dispersion can be understood to be a dispersion ofsilica in a fluid wherein weakened particle-to-particle repulsive forcesallow clustering of particles and formation of a silicaparticle-to-particle network or gel once the destabilized dispersion issubjected to an effective amount of shear. In certain cases, mechanicalshear may cause destabilization of silica dispersions and clustering ofsilica particles. The higher the degree of destabilization of silicaslurry, the lower the shear needed for aggregation of particles, and thehigher the rate of particle aggregation. For a destabilized dispersion,the dispersion can comprise from about 6 wt % to about 35 wt %particulate silica (based on the weight of the dispersion), e.g., fromabout 8 wt % to about 35 wt %, from about 10 wt % to about 28 wt %, fromabout 12 wt % to about 25 wt %, from about 15 wt % to about 30 wt %. Theaqueous fluid in the destabilized dispersion of silica particles may beor include water, an aqueous mixture, or a water miscible or partiallymiscible fluid, such as various alcohols, ethers, and other lowmolecular weight water-miscible solvents, preferably having C₁-C₅organic groups (e.g., ethanol, methanol, propanol, ethyl ether, acetone,and the like). To form silica elastomer composites, the stability ofsilica particles in a slurry or dispersion is reduced (i.e.,destabilized) by lowering the electrostatic energy barrier betweenparticles using an effective amount of a destabilizing agent such asacid or salt or both before the slurry is mixed with latex. Adestabilizing agent may be selected for its capacity to reduce repulsivecharge interaction among particle surfaces that prevent particles fromagglomeration in the fluid.

A destabilized dispersion of silica may be obtained by lowering the pHof the dispersion of silica to close to the isoelectric point of thesilica (around pH 2 for typical hydrophilic silicas). For example,destabilizing silica can be achieved by adding acid to lower a pH of thedispersion of particulate silica to 2 to 4, thus reducing the magnitudeof the zeta potential of the dispersion to less than 30 mV, such asbelow about 28 mV (e.g., zeta potentials of magnitude of about 18 mV toabout 6 mV for formic acid as the destabilization agent). The additionof acid and/or salt into silica slurry can effectively reduce thestability of silica particles dispersed in water. The acid or salt molarconcentration is generally the dominant factor that determines the zetapotential of the destabilized silica slurry. In general, a sufficientamount of acid or salt or both can be used to reduce the magnitude ofthe zeta potential of the silica slurry to less than 30 mV, such as 28mV or less, preferably 25 mV or less, for producing a semi-solid orsolid silica-containing continuous rubber phase.

The amount of acid used to destabilize the silica dispersion can be anamount to obtain a zeta potential magnitude in the destabilizeddispersion of less than 30 mV, such as 28 mV or less, or 25 mV or lower.The acid can be at least one organic or inorganic acid. The acid can beor include acetic acid, formic acid, citric acid, phosphoric acid, orsulfuric acid, or any combinations thereof. The acid can be or include aC₁ to C₄ alkyl containing acid. The acid can be or include one that hasa molecular weight or a weight average molecular weight below 200, suchas below 100 MW, or below 75 MW, or from about 25 MW to about 100 MW.The amount of acid can vary and depend on the silica dispersion beingdestabilized. The amount of acid can be, for instance, from about 0.8 wt% to about 7.5 wt %, for example, from about 1.5 wt % to about 7.5 wt %or more (based on the total weight of the fluid comprising thedispersion of silica). If an acid is the only destabilizing agent used,the amount of acid can be an amount that lowers the pH of the dispersionof silica by at least 2 pH units, or to at least a pH of 5 or lower, orthe pKa range of the acid or acids in use, so as to reduce chargeinteractions among particles.

A destabilized dispersion may be obtained by treating a dispersion ofsilica with a destabilizing agent comprising one or more salts to alterslurry zeta potential to the range described above. The salt can be orinclude at least one metal salt (e.g., from Group 1, 2, or 13 metals).The salt can be or include a calcium salt, magnesium salt, or aluminumsalt. Exemplary counterions include nitrate, acetate, sulfate, halogenions such as chloride, bromide, iodine, and the like. The amount of saltcan be, for instance, from about 0.2 wt % to about 2 wt % or more, forexample, from about 0.5 or 1 wt % to about 1.6 wt % (based on the weightof the fluid comprising the destabilized dispersion of silica).

A combination of at least one salt and/or at least one acid can be usedto destabilize the dispersion of the silica.

When the destabilized dispersion of silica is achieved with the additionof at least one salt, the salt concentration in the destabilizeddispersion of silica can be from about 10 mM to about 160 mM, or otheramounts above or below this range.

When the destabilized dispersion of silica is achieved with the additionof at least one acid, the acid concentration in the destabilizeddispersion can be from about 200 mM to about 1000 mM, for example, about340 mM to about 1000 mM, or other amounts above or below this range.

A destabilized silica dispersion may be made using silica particlestreated to comprise an appropriate amount of surface functional groupscarrying positive charges so that the net charges on the silica surfaceare reduced sufficiently to decrease the magnitude of zeta potential ofthe dispersion below 30 mV. The net charge on the silica surface can bepositive, instead of negative, as a result of such surface treatment.The positively charged functional group may be introduced to silicasurface through chemical attachment or physical adsorption. For example,the silica surface may be treated withN-trimethoxylsilylpropyl-N,N,N-trimethylammonium chloride either beforeor after preparation of the silica dispersion. It is also possible toadsorb cationic coating agents, such as amine containing molecules andbasic amino acids on the silica surface. It is theorized that a netpositive charge on silica particle surfaces may enhance coagulation ofthe latex, which comprises negatively charged rubber particles, by meansof heterocoagulation.

With regard to the “second fluid,” which contains at least one elastomerlatex, this fluid may contain one or more elastomer latices. Anelastomer latex can be considered a stable colloidal dispersion ofrubber and may contain, for example, from about 10 wt % to about 70 wt %rubber based on the total weight of the latex. The rubber can bedispersed in a fluid, such as water or other aqueous fluid, for example.The aqueous content of this fluid (or water content) can be 40 wt % orhigher, such as 50 wt % or higher, or 60 wt % or higher, or 70 wt % orhigher, for instance from about 40 wt % to 90 wt % based on the weightof the fluid comprising the at least one elastomer latex. Suitableelastomer latices include both natural and synthetic elastomer laticesand latex blends. For example, elastomer latex may be made syntheticallyby polymerizing a monomer such as styrene that has been emulsified withsurfactants. The latex should be appropriate for the wet masterbatchprocess selected and the intended purpose or application of the finalrubber product. It will be within the ability of those skilled in theart to select suitable elastomer latex or a suitable blend of elastomerlatices for use in the methods and apparatus disclosed here, given thebenefit of this disclosure.

The elastomer latex can be or include natural rubber, such as anemulsion of natural rubber. Exemplary natural rubber latices include,but are not limited to, field latex, latex concentrate (produced, forexample, by evaporation, centrifugation or creaming), skim latex (e.g.,the supernatant remaining after production of latex concentrate bycentrifugation) and blends of any two or more of these in anyproportion. Natural rubber latex typically is treated with ammonia topreserve it, and the pH of treated latex typically ranges from 9 to 11.The ammonia content of the natural rubber latex may be adjusted, and canbe reduced, e.g., by bubbling nitrogen across or through the latex.Typically, latex suppliers desludge the latex by addition of diammoniumphosphate. They may also stabilize the latex by addition of ammoniumlaurate. The natural rubber latex may be diluted to a desired dry rubbercontent (DRC). Thus, the latex that can be used here can be a desludgedlatex. A secondary preservative, a mixture of tetramethylthiuramdisulfide and zinc oxide (TZ solution) may also be included. The latexshould be appropriate for the wet masterbatch process selected and theintended purpose or application of the final rubber product. The latexis provided typically in an aqueous carrier liquid (e.g, water). Theamount of the aqueous carrier liquid can vary, and for instance be fromabout 30 wt % to about 90 wt % based on the weight of the fluid. Inother words, such natural rubber latices may contain, or may be adjustedto contain, e.g., about 10 wt % to about 70 wt % rubber. Selection of asuitable latex or blend of latices will be well within the ability ofthose skilled in the art given the benefit of the present disclosure andthe knowledge of selection criteria generally well recognized in theindustry.

The natural rubber latex may also be chemically modified in some manner.For example, it may be treated to chemically or enzymatically modify orreduce various non-rubber components, or the rubber molecules themselvesmay be modified with various monomers or other chemical groups such aschlorine. Epoxidized natural rubber latex may be especially beneficialbecause the epoxidized rubber is believed to interact with the silicasurface (Martin, et al., Rubber Chemistry and Technology, May 2015,doi:10.5254/rct15.85940). Exemplary methods of chemically modifyingnatural rubber latex are described in European Patent Publications Nos.1489102, 1816144, and 1834980, Japanese Patent Publications Nos.2006152211, 2006152212, 2006169483, 2006183036, 2006213878, 2006213879,2007154089, and 2007154095, Great Britain Patent No. GB2113692, U.S.Pat. Nos. 6,841,606 and 7,312,271, and U.S. Patent Publication No.2005-0148723. Other methods known to those of skill in the art may beemployed as well.

Other exemplary elastomers include, but are not limited to, rubbers,polymers (e.g., homopolymers, copolymers and/or terpolymers) of1,3-butadiene, styrene, isoprene, isobutylene,2,3-dialkyl-1,3-butadiene, where alkyl may be methyl, ethyl, propyl,etc., acrylonitrile, ethylene, propylene and the like. The elastomer mayhave a glass transition temperature (Tg), as measured by differentialscanning calorimetry (DSC), ranging from about −120° C. to about 0° C.Examples include, but are not limited to, styrene-butadiene rubber(SBR), natural rubber and its derivatives such as chlorinated rubber,polybutadiene, polyisoprene, poly(styrene-co-butadiene) and the oilextended derivatives of any of them. Blends of any of the foregoing mayalso be used. The latex may be in an aqueous carrier liquid. Particularsuitable synthetic rubbers include: copolymers of styrene and butadienecomprising from about 10 percent by weight to about 70 percent by weightof styrene and from about 90 to about 30 percent by weight of butadienesuch as a copolymer of 19 parts styrene and 81 parts butadiene, acopolymer of 30 parts styrene and 70 parts butadiene, a copolymer of 43parts styrene and 57 parts butadiene and a copolymer of 50 parts styreneand 50 parts butadiene; polymers and copolymers of conjugated dienessuch as polybutadiene, polyisoprene, polychloroprene, and the like, andcopolymers of such conjugated dienes with an ethylenic group-containingmonomer copolymerizable therewith such as styrene, methyl styrene,chlorostyrene, acrylonitrile, 2-vinyl-pyridine,5-methyl-2-vinylpyridine, 5-ethyl-2-vinylpyridine,2-methyl-5-vinylpyridine, allyl-substituted acrylates, vinyl ketone,methyl isopropenyl ketone, methyl vinyl either, alpha-methylenecarboxylic acids and the esters and amides thereof, such as acrylic acidand dialkylacrylic acid amide. Also suitable for use herein arecopolymers of ethylene and other high alpha olefins such as propylene,1-butene, and 1-pentene. Blends of two or more types of elastomer latex,including blends of synthetic and natural rubber latex or with two ormore types of synthetic or natural rubber, may be used as well.

The rubber compositions can contain, in addition to the elastomer andfiller and coupling agent, various processing aids, oil extenders,antidegradants, antioxidants, and/or other additives.

The amount of silica (in parts per hundred of rubber, or phr) present inthe elastomer composite can be from about 15 phr to about 180 phr, about20 phr to about 150 phr, about 25 phr to about 80 phr, about 35 phr toabout 115 phr, about 35 phr to about 100 phr, about 40 phr to about 100phr, about 40 phr to about 90 phr, about 40 phr to about 80 phr, about29 phr to about 175 phr, about 40 phr to about 110 phr, about 50 phr toabout 175 phr, about 60 phr to about 175 phr, and the like. Thesilica-reinforced elastomer composite may optionally include a smallamount of carbon black for color, conductivity, and/or UV stabilityand/or for other purposes. Small amounts of carbon black contained inthe elastomer composite can range, for instance, from about 0.1 wt % toabout 10 wt %, based on the weight of the total particles present in theelastomer composite. Any grade or type of carbon black(s) can be used,such as reinforcing, or semi-reinforcing tire-grade furnace carbonblacks and the like.

In any method of producing an elastomer composite, the method canfurther include one or more of the following steps, after formation ofthe solid or semi-solid silica-containing continuous rubber phase:

-   -   one or more holding steps or further solidification or        coagulation steps to develop further elasticity;    -   one or more dewatering steps can be used to de-water the        composite to obtain a de-watered composite;    -   one or more extruding steps;    -   one or more calendaring steps;    -   one or more milling steps to obtain a milled composite;    -   one or more granulating steps;    -   one or more baling steps to obtain a bailed product or mixture;    -   the baled mixture or product can be broken apart to form a        granulated mixture;    -   one or more mixing or compounding steps to obtain a compounded        composite.

As a further example, the following sequence of steps can occur and eachstep can be repeated any number of times (with the same or differentsettings), after formation of the solid or semi-solid silica-containingcontinuous rubber phase:

-   -   one or more holding steps or further coagulation steps to        develop further elasticity    -   dewatering the composite (e.g., the elastomer composite exiting        the reaction zone) to obtain a dewatered composite;    -   mixing or compounding the dewatered composite to obtain a        compounded mixture;    -   milling the compounded mixture to obtain a milled mixture (e.g.,        roll milling);    -   granulating or mixing the milled mixture;    -   optionally baling the mixture after the granulating or mixing to        obtain a baled mixture;    -   optionally breaking apart the baled mixture and mixing.

In any embodiment, a coupling agent can be introduced in any of thesteps (or in multiple steps or locations) as long as the coupling agenthas an opportunity to become dispersed in the elastomer composite.

As just one example, the solid or semi-solid silica-containingcontinuous rubber phase exiting the reaction zone or area can betransferred by a suitable apparatus (e.g., belt or conveyor), to adewatering extruder. Suitable dewatering extruders are well known andcommercially available from, for example, the French Oil Mill MachineryCo. (Piqua, Ohio, USA). Alternatively or in addition, the solid orsemi-solid silica-containing continuous rubber phase may be compressed,for example, between metallic plates, to expel at least a portion of theaqueous fluid phase, e.g., to expel aqueous fluid until the watercontent of such material is below 40 wt %.

In general, the post processing steps can comprise compressing theelastomer composite to remove from about 1 wt % to about 15 wt % ormore, of an aqueous fluid phase, based on the total weight of theelastomer composite. The dewatering extruder may bring the silicaelastomer composite from, e.g., approximately about 40% to about 95%water content to approximately about 5% to about 60% water content (forexample, from about 5% to about 10% water content, from about 10% toabout 20% water content, from about 15% to about 30% water content, orfrom about 30% to about 50% water content) with all weight percent basedon total weight of composite. The dewatering extruder can be used toreduce the water content of the silica elastomer composite to about 35wt % or other amounts. The optimal water content may vary with theelastomer employed, the amount, and/or type of filler, and the devicesemployed for mastication of the dewatered product. The elastomercomposite may be dewatered to a desired water content, following whichthe resulting dewatered product can be further masticated while beingdried to a desired moisture level (e.g., from about 0.5% to about 10%,for example, from about 0.5% to about 1%, from about 1% to about 3%,about 3% to about 5%, or from about 5% to about 10%, preferably below 1%all weight percent based on total weight of product). The mechanicalenergy imparted to the material can provide improvement in rubberproperties. For example, the dewatered product may be mechanicallyworked with one or more of a continuous mixer, an internal mixer, a twinscrew extruder, a single screw extruder, or a roll mill. This optionalmixing step can have the ability to masticate the mixture and/orgenerate surface area or expose surface which can permit removal ofwater (at least a portion thereof) that may be present in the mixture.Suitable masticating devices are well known and commercially available,including for example, a Unimix Continuous Mixer and MVX (Mixing,Venting, eXtruding) Machine from Farrel Corporation of Ansonia, Conn.,USA, a long continuous mixer from Pomini, Inc., a Pomini ContinuousMixer, twin rotor co-rotating intermeshing extruders, twin rotorcounter-rotating non-intermeshing extruders, Banbury mixers, Brabendermixers, intermeshing-type internal mixers, kneading-type internalmixers, continuous compounding extruders, the biaxial milling extruderproduced by Kobe Steel, Ltd., and a Kobe Continuous Mixer. Alternativemasticating apparatus will be familiar to those of skill in the art andcan be used.

As dewatered product is processed in a desired apparatus, the apparatusimparts energy to the material. Without being bound by any particulartheory, it is believed that friction generated during mechanicalmastication heats the dewatered product. Some of this heat is dissipatedby heating and vaporizing the moisture in the dewatered product. Aportion of the water may also be removed by squeezing the material inparallel with heating. The temperature should be sufficiently high torapidly vaporize water to steam that is released to the atmosphereand/or is removed from the apparatus, but not so high as to scorch therubber. The dewatered product can achieve a temperature from about 130°C. to about 180° C., such as from about 140° C. to about 160° C.,especially when the coupling agent is added prior to or duringmastication. The coupling agent can include a small amount of sulfur,and the temperature should be maintained at a sufficiently low level toprevent the rubber from cross-linking during mastication.

As an option, additives can be combined with the dewatered product in amechanical mixer. Specifically, additives such as filler (which may bethe same as, or different from, the filler used in the mixer; exemplaryfillers include silica, carbon black, and/or zinc oxide), otherelastomers, other or additional masterbatch, antioxidants, couplingagents, plasticizers, processing aids (e.g., stearic acid, which canalso be used as a curing agent, liquid polymers, oils, waxes, and thelike), resins, flame-retardants, extender oils, and/or lubricants, and amixture of any of them, can be added in a mechanical mixer. Additionalelastomers can be combined with the dewatered product to produceelastomer blends. Suitable elastomers include any of the elastomersemployed in latex form in the mixing process described above andelastomers such as EPDM that are not available in latex form and may bethe same or different than the elastomer in the silica-containingelastomer composite. Exemplary elastomers include, but are not limitedto, rubbers, polymers (e.g., homopolymers, copolymers and/orterpolymers) of 1,3-butadiene, styrene, isoprene, isobutylene,2,3-dialkyl-1,3-butadiene, where alkyl may be methyl, ethyl, propyl,etc., acrylonitrile, ethylene, propylene, and the like. Methods ofproducing masterbatch blends are disclosed in commonly owned U.S. Pat.Nos. 7,105,595, 6,365,663, and 6,075,084 and PCT PublicationWO2014/189826. The antioxidant (an example of a degradation inhibitor)can be an amine type antioxidant, phenol type antioxidant, imidazoletype antioxidant, metal salt of carbamate, para-phenylene diamine(s)and/or dihydrotrimethylquinoline(s), polymerized quinine antioxidant,and/or wax and/or other antioxidants used in elastomer formulations.Specific examples include, but are not limited to,N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6-PPD, e.g.,ANTIGENE 6C , available from Sumitomo Chemical Co., Ltd. and NOCLAC 6C,available from Ouchi Shinko Chemical Industrial Co., Ltd.), “Ozonon” 6Cfrom Seiko Chemical Co., Ltd., polymerized 1,2-dihydro-2,2,4-trimethylquinoline (TMQ, e.g., Agerite Resin D, available from R. T. Vanderbilt),2,6-di-t-butyl-4-methylphenol (available as Vanox PC from VanderbiltChemicals LLC), butylhydroxytoluene (BHT), and butylhydroxyanisole(BHA), and the like. Other representative antioxidants may be, forexample, diphenyl-p-phenylenediamine and others such as, for example,those disclosed in The Vanderbilt Rubber Handbook (1978), pages 344-346.

The coupling agent can be or include one or more silane coupling agents,one or more zirconate coupling agents, one or more titanate couplingagents, one or more nitro coupling agents, or any combination thereof.The coupling agent can be or includebis(3-triethoxysilylpropyl)tetrasulfane (e.g., Si 69 from EvonikIndustries, Struktol SCA98 from Struktol Company),bis(3-triethoxysilylpropyl)disulfane (e.g., Si 75 and Si 266 from EvonikIndustries, Struktol SCA985 from Struktol Company),3-thiocyanatopropyl-triethoxy silane (e.g., Si 264 from EvonikIndustries), gamma-mercaptopropyl-trimethoxy silane (e.g., VP Si 163from Evonik Industries, Struktol SCA989 from Struktol Company),gamma-mercaptopropyl-triethoxy silane (e.g., VP Si 263 from EvonikIndustries), zirconium dineoalkanolatodi(3 -mercapto) propionato-O,N,N′-bis(2-methyl-2-nitropropyl)-1,6-diaminohexane,S-(3-(triethoxysilyl)propyl) octanethioate (e.g., NXT coupling agentfrom Momentive, Friendly, WV), and/or coupling agents that arechemically similar or that have the one or more of the same chemicalgroups. Additional specific examples of coupling agents, by commercialnames, include, but are not limited to, VP Si 363 from EvonikIndustries. It is to be appreciated that any combination of elastomers,additives, and additional masterbatch may be added to the dewateredproduct, for instance in a compounder.

As an option, the dewatered product can be masticated using an internalmixer such as a Banbury or Brabender mixer. The dewatered product mayfirst be brought to a moisture content of about 3 wt % to about 40 wt %,for example, about 5 wt % to about 20 wt %, or about 20 wt % to about 30wt %. The moisture content may be achieved by dewatering to the desiredlevel or by dewatering the dewatered product crumb to an intermediatemoisture content as the first step and then further reducing moisturecontent by heating the resulting dewatered product, or by letting waterevaporate from the dewatered product at room temperature, or by othermethods familiar to those of skill in the art. The dewatered product maythen be masticated in an internal mixer until a desired moisture levelor mechanical energy input is achieved. The dewatered product can bemasticated until it reaches a predetermined temperature, allowed tocool, and then placed back into the internal mixer one or more times toimpart additional energy to the material. Examples of temperaturesinclude from about 140° C. to about 180° C., for example, from about145° C. to about 160° C., or from about 150° C. to about 155° C. Thedewatered product may be sheeted in a roll mill after each masticationin the internal mixer. Alternatively or in addition, dewatered productthat has been masticated in a Banbury or Brabender mixer may be furthermasticated in an open mill.

As an option, the masticated product can be further processed on an openmill. The masticated product can be discharged from the continuouscompounder as a length of extrudate and may be cut into smaller lengthsprior to entering the open mill. The masticated product may optionallybe fed to the open mill via a conveyor. The conveyor may be a conveyorbelt, conduit, pipe, or other suitable means for transporting themasticated product from a continuous compounder to an open mill. Theopen mill can include a pair of rollers that may optionally be heated orcooled to provide enhanced operation of the open mill. Other operatingparameters of the open mill can include the gap distance between therolls, the bank height, i.e., the reservoir of material in the gapbetween and on top of the rolls, and the speed of each roll. The speedof each roll and the temperature of the fluid used to cool each roll maybe controlled independently for each roll. The gap distance may be fromabout 3 mm to about 10 mm or from about 6 mm to about 8 mm. The rollspeed may be about 15 rpm to about 70 rpm, and the rollers may rolltowards one another with respect to the inlet side of the mill. Thefriction ratio, the ratio of the speed of the collection roller, e.g.,the roller on which the masticated product collects, to that of the backroller, may be from about 0.9 to about 1.1. The fluid employed to coolthe rollers may be from about 35° C. to about 90° C., for example, fromabout 45° C. to about 60° C., from about 55° C. to about 75° C., or fromabout 70° C. to about 80° C. In addition to controlling the operation ofthe open mill to provide a desired level of mastication and desiccationto the masticated product, it is also desirable that the output of theopen mill should collect on the collection roller as a smooth sheet.Without being bound by any particular theory, it is thought that coolerroller temperatures facilitate this goal. The open mill may reduce thetemperature of the masticated product to approximately about 110 ° C. toabout 140° C. The residence time of the masticated product in the millcan be determined in part by the roller speed, the gap distance and theamount of mastication and drying desired and may be about 10 minutes toabout 20 minutes for material that has already been masticated, forexample, in a twin-rotor continuous mixer.

One skilled in the art will recognize that different combinations ofdevices may be employed to provide mastication and desiccation to asolid silica-containing continuous rubber phase produced according tothe various embodiments. Depending on which devices are used, it may bedesirable to operate them under different conditions than thosedescribed above to impart varying amounts of work and desiccation to thematerial. In addition, it may be desirable to employ more than oneparticular kind of device, e.g., an open mill or internal mixer, inseries or to pass masticated product through a given device more thanone time. For example, the masticated product may be passed through anopen mill two or three or more times or passed through two or three ormore open mills in series. In the latter case, it may be desirable tooperate each open mill under different operating conditions, e.g.,speed, temperature, different (e.g. higher) energy input, etc.Masticated product can be passed through one, two, or three open millsafter being masticated in an internal mixer.

The elastomer composite may be used to produce an elastomer or rubbercontaining product. As an option, the elastomer composite may be used inor produced for use in various parts of a tire, for example, tires, tiretreads, tire sidewalls, wire-skim for tires, and cushion gum for retreadtires. Alternatively or in addition, elastomer composite may be used forhoses, seals, gaskets, anti-vibration articles, tracks, track pads fortrack-propelled equipment such as bulldozers, etc., engine mounts,earthquake stabilizers, mining equipment such as screens, miningequipment linings, conveyor belts, chute liners, slurry pump liners, mudpump components such as impellers, valve seats, valve bodies, pistonhubs, piston rods, plungers, impellers for various applications such asmixing slurries and slurry pump impellers, grinding mill liners,cyclones and hydrocyclones, expansion joints, marine equipment such aslinings for pumps (e.g., dredge pumps and outboard motor pumps), hoses(e.g., dredging hoses and outboard motor hoses), and other marineequipment, shaft seals for marine, oil, aerospace, and otherapplications, propeller shafts, linings for piping to convey, e.g., oilsands and/or tar sands, and other applications where abrasion resistanceand/or enhanced dynamic properties are desired. The vulcanized elastomercomposite may be used in rollers, cams, shafts, pipes, tread bushingsfor vehicles, or other applications where abrasion resistance and/orenhanced dynamic properties are desired.

Traditional compounding techniques may be used to combine vulcanizationagents and other additives known in the art, including the additivesdiscussed above in connection with the dewatered product, with the driedelastomer composite, depending on the desired use.

The present invention further relates to an elastomer composite formedby any one or more methods described herein of the present invention.

Unless otherwise specified, all material proportions described as apercent herein are in weight percent.

The present invention will be further clarified by the followingexamples which are intended to be only exemplary in nature.

EXAMPLES

In these examples, the “field latex” was field latex (Muhibbah LateksSdn Bhd, Malaysia) having a dry rubber content of about 30 wt %. The“latex concentrate” was latex concentrate (high ammonia grade, fromMuhibbah Lateks Sdn Bhd, Malaysia, or from Chemionics Corporation,Tallmadge, Ohio) diluted by about 50% to a dry rubber content of about30 wt % using either pure water or water with 0.6 wt % to 0.7 wt %ammonia. Unless noted otherwise, the “silica” was ZEOSIL® Z1165 MPprecipitated silica from Solvay USA Inc., Cranbury, N.J. (formerlyRhodia).

Thermogravimetric Analysis. The actual silica loading levels weredetermined by thermogravimetric analysis (TGA) following the ISO 6231method.

Water Content of Product. The test material was cut into mm size piecesand loaded into the moisture balance (e.g., Model MB35 and Model MB45;Ohaus Corporation, Parsippany N.J.) for measurement. The water contentwas measured at 130° C. for 20 minutes to 30 minutes until the testsample achieved a consistent weight.

Slurry Zeta Potential. In these examples, the zeta potential ofparticulate slurries was measured using a ZetaProbe Analyzer™ fromColloidal Dynamics, LLC, Ponte Vedra Beach, Fla. USA. Withmulti-frequency electroacoustic technology, the ZetaProbe measures zetapotential directly at particle concentrations as high as 60% by volume.The instrument was first calibrated using the KSiW calibration fluidprovided by Colloidal Dynamics (2.5 mS/cm). A 40 g sample was thenplaced into a 30 mL Teflon cup (Part #A80031) with a stir bar, and thecup was placed on a stirring base (Part #A80051) with 250 rpm stirringspeed. The measurement was performed using the dip probe 173 in asingle-point mode with 5-point run at ambient temperature (approximately25 ° C.). The data were analyzed using ZP version 2.14 c Polar™ softwareprovided by Colloidal Dynamics. The zeta potential values can benegative or positive depending on polarity of charge on the particles.The “magnitude” of zeta potential refers to the absolute value (e.g., azeta potential value of −35 mV has a higher magnitude than a zetapotential value of −20 mV). The magnitude of the zeta potential reflectsthe degree of electrostatic repulsion between similarly chargedparticles in dispersion. The higher the magnitude of zeta potential, themore stable of particles in dispersion. Zeta potential measurements werecarried out on particulate silica slurries prepared as described below.

Dry silica was weighed and combined with deionized water using a5-gallon bucket and a high shear overhead laboratory mixer with ashrouded agitator (Silverson Model AX3, Silverson Machines, Inc., EastLongmeadow, Mass.; operating at 5200-5400 rpm for 30 minutes to 45minutes). Once the silica was roughly dispersed in water and able to bepumped, the silica slurry was transferred via a peristaltic pump(Masterflex 7592-20 system—drive and controller, 77601-10 pump headusing I/P 73 tubing; Cole-Palmer, Vernon Hills, Ill.) into a mixing loopwith an inline high shear rotor-stator mixer (Silverson Model 150LBlocated after the peristaltic pump, operated at 60 Hz) in a run tank (30gal. convex bottom port vessel) and was ground to further break downsilica agglomerates and any remaining silica granules. The slurry in therun tank was then circulated at 2 L/min using the same peristaltic pumpthrough the mixing loop for a time sufficient for turnover of at least5-7 times of the total slurry volume (>45 minutes) to make sure anysilica agglomerates were properly ground and distributed. An overheadmixer (Ika Eurostar power control visc-P7; IKA-Works, Inc., Wilmington,N.C.) with a low shear anchor blade rotating at about 60 rpm was used inthe run tank to prevent gelling or sedimentation of silica particles. Anacid (formic acid or acetic acid, reagent grade from Sigma Aldrich, St.Louis, Mo.) or salt (calcium nitrate, calcium chloride, calcium acetateor aluminum sulfate, reagent grade from Sigma Aldrich, St. Louis, Mo.)was added to the slurry in the run tank after grinding. The amount ofsilica in the slurry and the type and concentration of acid or salt areindicated in the specific Examples below.

Exemplary Process A. Where indicated in the examples below, a method wascarried out utilizing Exemplary Process A. In Process A, dryprecipitated silica and water (municipal water filtered to removeparticulate matter) were metered and combined and then ground in arotor-stator mill to form silica slurry, and the silica slurry wasfurther ground in a feed tank using an agitator and another rotor-statormill. The silica slurry was then transferred to a run tank equipped withtwo stirrers. The silica slurry was recirculated from the run tankthrough a homogenizer and back into the run tank. A solution of acid(formic acid or acetic acid, industrial grade obtained from Kong LongHuat Chemicals, Malaysia) or salt (calcium nitrate, industrial gradeobtained from Mey Chern Chemicals, Malaysia) was then pumped into therun tank. The slurry was maintained in dispersed form through stirringand, optionally, by means of the recirculating loop in the run tank.After a suitable period, the silica slurry was fed to a confinedreaction zone (13), such as the one shown in FIG. 1A, by means of thehomogenizer. The concentration of silica in the slurry and theconcentration of acid or calcium nitrate are indicated in the specificExamples below.

The latex was pumped with a peristaltic pump (at less than about 40 psigpressure) through the second inlet (11) into the reaction zone (13). Thelatex flow rate was adjusted between about 300-1600 kg latex/hr in orderto obtain a desired production rate and silica loading levels in theresulting product. The homogenized slurry containing acid, or salt, or acombination of acid and salt, was pumped under pressure from thehomogenizer to a nozzle (0.060″-0.130″ inside diameter (ID)) (3 a),represented by the first inlet (3) shown in FIG. 1A, such that theslurry was introduced as a high speed jet into the reaction zone. Uponcontact with the latex in the reaction zone, the jet of silica slurryflowing at a velocity of 25 m/s to 120 m/s entrained the latex flowingat 1 m/s to 11 m/s. In Examples according to embodiments of theinvention, the impact of the silica slurry on the latex caused anintimate mixing of silica particles with the rubber particles of thelatex, and the rubber was coagulated, transforming the silica slurry andthe latex into a material comprising a solid or semi-solidsilica-containing continuous rubber phase containing 40 to 95 wt %water, based on total weight of the material, trapped within thematerial. Adjustments were made to the silica slurry flow rate (500-1800kg/hr), or the latex flow rate (300-1800 kg/hr), or both, to modify thesilica to rubber ratios (e.g., 15-180 phr silica) in the final product,and to achieve the desired production rate. The production rates (drymaterial basis) were 200-800 kg/hr. Specific silica contents (by TGAanalysis) in the rubber following dewatering and drying of the materialare listed in the Examples below.

Process A Dewatering. Material was discharged from the reaction zone atatmospheric pressure at a flow rate from 200 to 800 kg/hr (dry weight)into a dewatering extruder (The French Oil Machinery Company, Piqua,Ohio). The extruder (8.5 inch I.D.) was equipped with a die plate withvarious die-hole buttons configurations and operated at a typical rotorspeed of 90 to 123 RPM, die plate pressure 400-1300 psig, and power of80 kW to 125 kW. In the extruder, silica-containing rubber wascompressed, and the water squeezed out of the silica-containing rubberwas ejected through a slotted barrel of the extruder. Dewatered producttypically containing 15-60 wt % water was obtained at the outlet of theextruder.

Process A Drying and Cooling. The dewatered product was dropped into acontinuous compounder (Farrel Continuous Mixer (FCM), FarrelCorporation, Ansonia, CT; with #7 and 15 rotors) where it was dried,masticated and mixed with 1-2 phr of antioxidant (e.g. 6PPD fromFlexsys, St. Louis, Mo.) and optionally silane coupling agent (e.g. NXTsilane, obtained from Momentive Performance Materials, Inc., Waterford,N.Y.; 8 wt % silane on silica weight basis). The temperature of the FCMwater jacket was set at 100° C., and the FCM temperature at the outputorifice was 140° C. to 180° C. The moisture content of the masticated,dewatered elastomer composite exiting the FCM was around 1 wt % to 5 wt%. The product was further masticated and cooled on an open mill. Arubber sheet of the elastomer composite was directly cut from the openmill, rolled and cooled in air.

Exemplary Process B. Where indicated in the examples below, an exemplarymethod was carried out utilizing Exemplary Process B. In Process B, drysilica was weighed and combined with deionized water using a 5-gallonbucket and a high shear overhead laboratory mixer with a shroudedagitator (Silverson Model AX3, Silverson Machines, Inc., EastLongmeadow, Mass.; operating at 5200 rpm to 5400 rpm for 30-45 minutes).Once the silica was roughly dispersed in water and able to be pumped,the silica slurry was transferred via a peristaltic pump (Masterflex7592-20 system—drive and controller, 77601-10 pump head using I/P 73tubing; Cole-Palmer, Vernon Hills, Ill.) into a mixing loop with aninline high shear rotor-stator mixer (Silverson Model 150LB locatedafter the peristaltic pump, operated at 60 Hz) in a run tank (30 galconvex bottom port vessel) and was ground to further break down silicaagglomerates and any remaining granules. The slurry in the run tank wasthen circulated at 2 L/min through the mixing loop for a time sufficientfor turnover of at least 5-7 times of the total slurry volume (>45minutes) to make sure any silica agglomerates were properly ground anddispersed. An overhead mixer (Ika Eurostar power control visc-P7;IKA-Works, Inc., Wilmington, N.C.) with a low shear anchor bladerotating at about 60 rpm was used in the run tank to prevent gelling orsedimentation of silica particles. An acid (formic acid or acetic acid,reagent grade from Sigma Aldrich, St. Louis, Mo.) or salt (calciumnitrate, calcium chloride, calcium acetate, or aluminum sulfate salt,reagent grade from Sigma Aldrich, St. Louis, Mo.) was added to theslurry in the run tank after grinding. The amount of silica in theslurry and the type and concentration of acid or salt are indicated inTable 4 for the specific Examples below.

The latex was pumped using a peristaltic pump (Mastedlex 7592-20system—drive and controller, 77601-10 pump head using I/P 73 tubing;Cole-Palmer, Vernon Hills, Ill.) through a second inlet (11) and into areaction zone (13) configured similarly to that shown in FIG. 1B. Thelatex flow rate was adjusted between about 25 kg/h to about 250 kg/h inorder to modify silica to rubber ratios of the elastomer composites.

When the silica was well dispersed in the water, the slurry was pumpedfrom the run tank through a diaphragm metering pump (LEWA-NikkisoAmerica, Inc., Holliston, Mass.) through a pulsation dampener (to reducepressure oscillation due to the diaphragm action) into either thereaction zone or the run tank via a recycle loop “T” connector. Thedirection of the slurry was controlled by two air actuated ball valves,one directing the slurry to the reaction zone and the other directingthe slurry to the run tank. When ready to mix the silica slurry withlatex, the line feeding the first inlet (3) to the reaction zone waspressurized to 100 psig to 150 psig by closing both valves. The ballvalve directing the slurry to the reaction zone was then opened andpressurized silica slurry was fed to a nozzle (0.020′ to 0.070″ ID) (3a) shown in FIG. 1B, at an initial pressure of 100 psig to 150 psig,such that the slurry was introduced as a high speed jet into thereaction zone. Upon contact with the latex in the reaction zone, the jetof silica slurry flowing at a velocity of 15 m/s to 80 m/s entrained thelatex flowing at 0.4 m/s to 5 m/s. In Examples according to embodimentsof the invention, the impact of the silica slurry on the latex caused anintimate mixing of silica particles with the rubber particles of thelatex, and the rubber was coagulated, transforming the silica slurry andthe latex into an elastomer composite comprising the silica particlesand 40 wt % to 95 wt % water trapped within a solid or semi-solidsilica-containing, continuous rubber phase. Adjustments were made to thesilica slurry flow rate (40 kg/hr to 80 kg/hr) or the latex flow rate(25 kg latex/hr to 300 kg latex/hr), or both, to modify silica to rubberratios (e.g., 15 phr to 180 phr silica) in the resulting product and toachieve the desired continuous production rates (30 kg/hr to 200 kg/hron dry material basis). Specific silica to rubber ratio (phr) contentsfollowing dewatering and drying are listed in the Examples below.

Process B Dewatering.

Material discharged from the reaction zone was recovered and sandwichedbetween two aluminum plates inside a catch pan. The “sandwich” was theninserted between two platens of a hydraulic press. With 2500 psigpressure exerted on the aluminum plates, water trapped inside the rubberproduct was squeezed out. If needed, the squeezed material was foldedinto a smaller piece and the squeezing process was repeated using thehydraulic press until the water content of the rubber product was below40 wt %.

Process B Drying and Cooling. The dewatered product was put into aBrabender mixer (300 cc) for drying and mastication to form amasticated, dewatered elastomer composite. Sufficient dewatered materialwas charged into the mixer to cover the rotors. The initial temperatureof the mixer was set at 100° C. and the rotor speed was generally at 60rpm. The water remaining in the dewatered product was converted to steamand evaporated out of the mixer during the mixing process. As thematerial in the mixer expanded as result of evaporation, any overflowingmaterial was removed as necessary. Either or both of a silane couplingagent (NXT silane, obtained from Momentive Performance Materials, Inc.,Waterford, N.Y.; 8 wt % silane on silica weight basis) and/orantioxidant (6-PPD, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine,Flexsys, St. Louis, Mo.) was optionally added to the mixer when themixer temperature was above 140° C. When the temperature of the mixerreached 160° C., the material inside the mixer was held at 160° C. to170° C. by varying the rotor speed for 2 minutes before the material wasdumped. The masticated, dewatered elastomer composite was then processedon an open mill. The moisture content of the material being taken off ofthe mill typically was below 2 wt %.

Preparation of Rubber Compounds.

Dried elastomer composite obtained by either Process A or Process B wascompounded according to the formulation in Table A and the procedureoutlined in Table B. For silica elastomer composites where either silaneor antioxidant was added during drying, the final compound compositionis as specified in Table A. The amount of silane coupling agent and/orantioxidant added during compounding was adjusted accordingly.

TABLE A Ingredient phr NR in Composite 100 Silica in Composite S 6PPD*(antioxidant) 2.0 Silane (NXT silane**) 0.08 × (phr silica) ZnO 4Stearic acid 2 DPG*** 1.5 Cure Rite ® BBTS**** 1.5 Sulfur 1.5*N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (Flexsys, St. Louis,MO) **main active component: S-(3-(triethoxysilyl)propyl)octanethioate(Momentive, Friendly, WV) ***DiphenylGuanidine (Akrochem, Akron, OH)****N-tert-Butylbenzothiazole-2-sulphenamide (Emerald PerformanceMaterials, Cuyahoga Falls, OH) NR = natural rubber S = as stated

TABLE B Time (min) Operation Stage 1 Brabender mixer (300 cc), 65% fillfactor, 60 rpm, 100° C. 0 Add rubber-silica composite 1 Add silanecoupling agent, if needed Hold for 2 minutes beginning at 150° C. 2Sweep and add 6PPD and mix for 1 additional minute at 150° C. 3 SweepDump, 160° C. Pass through roll mill 6x Stage 2 Brabender mixer (300cc), 63% fill factor, 60 rpm, 100° C. 0 Add stage 1 compound 1 Add zincoxide and stearic acid 2 Sweep 4 Dump, 150° C. Pass through roll mill 6xStage 3 Brabender mixer (300 cc), 63% fill factor, 60 rpm, 100° C. 0 Addstage 2 compound, sulfur and accelerators 0.5 Sweep 1 Dump Roll mill forone minute with adequate band. Remove and perform 6 end rolls. Sheet offto required thickness.

Vulcanization was carried out in a heated press set at 150° C. for atime determined by a conventional rubber rheometer (i.e., T90+10% ofT90, where T90 is the time to achieve 90% vulcanization).

Properties of Rubber/Silica Compounds.

The tensile properties of vulcanized samples (T300 and T100, elongationat break, tensile strength) were measured according to ASTM standardD-412. Tan delta 60° was determined using a dynamic strain sweep intorsion between 0.01% and 60% at 10 Hz and 60° C. Tan δ_(max) was takenas the maximum value of tan 6 60within this range of strains.

Example 1

A silica slurry with 27.8 wt % Zeosil® 1165 silica was prepared asdescribed above in connection with the Slurry Zeta Potential testmethod. The slurry was then diluted using either deionized water or asupernatant obtained from ultracentrifugation of the 27.8 wt % slurry tomake a series of silica slurries at various silica concentrations. Thezeta potential of various silica slurries was measured to show therelationship between the concentration of the silica in the slurry andthe zeta potential of the slurry. The zeta potential of the silicaslurry, as shown in Table 1, appears to depend upon the silicaconcentration when the silica slurry is made using deionized water.However, as shown in Table 2, when slurry was diluted using thesupernatant obtained from ultracentrifugation of the 27.8 wt % slurry,the zeta potential stays roughly the same at different silicaconcentrations.

TABLE 1 Zeta potential of slurry of silica made using deionized water.Silica 6% 10% 15% 20% 22% 25% Concentration in slurry (w/w) ZetaPotential −46.4 −42.7 −39.6 −36.2 −34.7 −32.3 (mV) pH 5.19 5.04 4.924.86 4.83 4.77

TABLE 2 Zeta potential of silica slurry made from dilution of a 27.8 wt% silica slurry using the supernatant of the 27.8 wt % silica slurry.Silica Concentration in slurry (w/w) 6% 22% Zeta Potential (mV) −31.5−31.4 pH 4.86 4.79

This result demonstrates that an increase of magnitude of zeta potentialwhen such silica slurries are diluted with deionized water is mostly dueto reduction of ionic strength of the slurry. The ions in the silicaslurry are believed to be from residual salts present in the silica fromthe silica particle manufacturing process. The high magnitude of zetapotential of the silica slurries (all over 30 mV) indicated that thesilica has high electrostatic stability in the slurry.

Example 2

The effect of adding salt or acid at various concentrations to silicaslurries on the zeta potential of these slurries is set forth in Table3. Slurries were prepared in deionized water by the Slurry ZetaPotential test method described above. Data summarized in Table 3illustrate the dependence of zeta potential of silica slurries anddestabilized silica slurries on the silica concentration, saltconcentration, and acid concentration. Adding salt or acid to silicaslurry reduces the magnitude of zeta potential, thus the stability ofthe silica slurry. As shown in Table 3, the zeta potential dependsmostly on the concentration of salt or acid in the slurry ordestabilized slurry, and not on silica concentration.

TABLE 3 Zeta potential of slurry and destabilized of silica at variousslurry concentrations, salt concentrations, and acid concentrations.[acetic [formic Silica Concentration [CaCl₂] acid] acid] Zeta in Slurry(wt %) (mM) (mM) (mM) (mV) pH 22.0 0 0 0 −34.4 4.80 6.0 0 0 0 −45.0 ND22.0 10.6 0 0 −24.2 4.49 22.0 29.7 0 0 −17.0 4.27 22.0 51.1 0 0 −14.64.17 22.0 105 0 0 −9.2 ND 22.0 155 0 0 −6.4 ND 6.0 4.6 0 0 −29.9 ND 6.010.4 0 0 −23.4 ND 6.0 27.6 0 0 −18.5 ND 6.0 46.4 0 0 −15.4 ND 6.0 140 00 −7.7 ND 22.0 0 98 0 −23.6 3.72 22.0 0 192 0 −21.4 3.65 22.0 0 564 0−17.1 3.26 22.0 0 1857 0 −12.7 ND 6.0 0 27 0 −33.6 3.84 6.0 0 45 0 −29.93.68 6.0 0 174 0 −22.1 3.38 6.0 0 431 0 −18.9 3.61 22.0 0 0 118 −15.33.17 22.0 0 0 197 −14.2 2.96 22.0 0 0 731 −10.7 2.46 22.0 0 0 1963 −6.52.04 6.0 0 0 36 −17.7 3.07 6.0 0 0 42 −17.4 3.04 6.0 0 0 168 −14.6 2.626.0 0 0 456 −11.4 2.29 22.0 10.7 0 130 −12.9 3.04 22.0 26.6 0 248 −9.02.78 22.0 101 0 978 −3.1 2.10 6.0 4.7 0 36 −15.9 3.12 6.0 46.4 0 224−10.1 2.41 ND = not determined.

Results shown in Table 3 illustrate the dependence of zeta potential ofsilica slurries and destabilized silica slurries on acetic acidconcentration and silica concentration. The data show that the zetapotential values are more dependent on the acid concentration than thesilica concentration. A similar relationship between zeta potential toacid concentration and silica concentration is observed for formic acid.At a given concentration, formic acid reduces zeta potential magnitudemore than acetic acid. As shown in Table 3, a combination of formic acidand calcium chloride was effective in reducing the zeta potentialmagnitude. The results in Table 3 show that the stability of silicaparticles in slurry can be reduced effectively through addition ofdestabilization agents, such as acid or salt or a combination of acidand salt. Similar results were seen for calcium nitrate and calciumacetate.

Example 3

In this example, the importance of destabilizing the dispersion ofsilica particles prior to contacting the silica dispersion withelastomer latex was established. Specifically, four experiments were runusing the mixing apparatus of FIG. 1C, equipped with three inlets (3,11, 14) for introducing up to three fluids into a confined reaction zone(13), such that one fluid impacted the other fluids at a 90 degree angleas a high speed jet at a velocity of 15 m/s to 80 m/s (See FIG. 1C). Inthree of the four experiments, the silica was ground as described abovein Process B and acetic acid was optionally added as described inExamples 3-A to 3-D, below. The slurry or destabilized slurry was thenpressurized to 100 psig to 150 psig and fed into the confined reactionzone through the inlet (3) at a volumetric flow rate of 60 liter perhour (L/hr) such that the slurry or destabilized slurry was introducedas a high speed jet at 80 m/s into the reaction zone. At the same time,natural rubber latex concentrate (60CX12021 latex, 31 wt % dry rubbercontent, from Chemionics Corporation, Tallmadge, Ohio, diluted withdeionized water) was introduced into the second inlet (11) through aperistaltic pump at a volumetric flow rate of 106 L/hr and velocity of1.8 m/s. These rates were selected and flows were adjusted to yield anelastomer composite product comprising 50 phr (parts per hundred weightdry rubber) silica. The silica slurry or destabilized silica slurry andlatex were mixed by combining the low velocity latex flow and the highvelocity jet of silica slurry or destabilized slurry through entrainingthe latex flow in the jet of silica slurry or destabilized silica slurryat the point of impact. The production rate (on a dry material basis)was set at 50 kg/hr. Specific actual silica to rubber ratios in rubbercomposites produced by the process are listed in the Examples below. TGAwas performed following drying according to the Process B method.

Example 3-A

First Fluid: A destabilized aqueous dispersion of 25 wt % of silica with6.2 wt % (or 1.18 M) acetic acid was prepared as described in Process Bdescribed above. The zeta potential of the destabilized slurry was −14mV, indicating that the slurry was significantly destabilized by theacid. The destabilized silica slurry was pumped continuously underpressure into the first inlet (3).

Second Fluid: Elastomer latex was supplied to the reaction zone throughthe second inlet (11).

The first fluid impacted the second fluid in the reaction zone.

Results: A liquid to solid phase inversion occurred in the reaction zonewhen the destabilized silica slurry and latex were intimately mixed byentraining the low velocity latex flow into the high velocity jet ofdestabilized silica slurry. During the entrainment process, the silicawas intimately distributed into the latex and the mixture coagulatedinto a solid phase which contained 70 wt % to 85 wt % of water. As aresult, a flow of a solid silica-containing, continuous rubber phase ina worm or rope-like shape was obtained at the outlet of the reactionzone (13). The composite was elastic and could be stretched to 130% ofthe original length without breaking. TGA analysis on the dried productshowed the elastomer composite contained 58 phr of silica.

Example 3-B

First Fluid: A destabilized aqueous dispersion of 25 wt % of silica with6.2 wt % acetic acid was prepared according to Process B describedabove. The zeta potential of the slurry was −14 mV, indicating theslurry was significantly destabilized by the acid. The destabilizedsilica slurry was pumped continuously under pressure into the firstinlet (3).

Second Fluid: Elastomer latex was supplied to the reaction zone throughthe second inlet (11).

Third Fluid: Deionized water was also injected into the reaction zonethrough third inlet (14) at a volumetric flow rate of 60 L/hr and avelocity of 1.0 m/s.

The three fluids met and impacted each other in the reaction zone.

Results: A liquid to solid phase inversion occurred in the reaction zoneand a solid or semi-solid silica containing continuous rubber phase in arope or worm-like shape was obtained from the outlet of the reactionzone. A significant amount of cloudy liquid containing silica and/orlatex flowed out of the outlet (7) with the solid or semi-solidsilica-containing continuous rubber phase. The silica-containingcontinuous rubber phase contained about 70 wt % to about 75 wt % waterbased on the weight of the composite. TGA analysis on the dried productshowed the elastomer composite contained 44 phr of silica. Thus, theaddition of water through the third inlet had a negative impact on theprocess, yielding a product with lower silica content (44 phr incontrast to 58 phr in Example 3-A) and significant waste product.

Example 3-C

First Fluid: A 10 wt % acetic acid aqueous solution without silica wasprepared. A continuous feed of the acid fluid was pumped using aperistaltic pump at a volumetric flow rate of 60 L/hr through the thirdinlet (14) into the reaction zone at a velocity of 1.0 m/s at the timeof entry into the reaction zone.

Second Fluid: Elastomer latex was supplied to the reaction zone throughthe second inlet (11) by a peristaltic pump at a velocity of 1.8 m/s anda volumetric flow rate of 106 L/hr.

The two fluids met and impacted each other in the reaction zone.

Results: A solid worm-like, sticky rubber phase was formed. TGA analysison the dried product showed the solid rubber phase contained no silica.

Example 3-D

First Fluid: An aqueous dispersion of 25 wt % of silica without aceticacid was prepared according to Process B described above. The silicaslurry was pumped under pressure continuously into the first inlet (3)at a volumetric flow rate of 60 L/hr and at a velocity of 80 m/s at thepoint of entry into the reaction zone. The zeta potential of the slurrywas −32 mV, indicating that silica was stably dispersed in the slurry.Thus, in this Example 3-D, the silica slurry was not destabilized byaddition of acid to the slurry prior to impacting the latex fluid.

Second Fluid: Elastomer latex was supplied to the reaction zone throughthe second inlet (11) by a peristaltic pump at a velocity of 1.8 m/s anda volumetric flow rate of 106 L/hr.

Third fluid: After an initial period of continuous flow of the first andsecond fluids, a 10 wt % acetic acid aqueous solution was injectedthrough the third inlet (14) into the reaction zone at a volumetric flowrate that increased from 0 L/hr to 60 L/hr and a velocity that increasedfrom 0 m/s to 1.0 m/s. All three fluids impacted each other and mixed inthe reaction zone.

Results: Initially, prior to the injection of acid, no silica-containingcontinuous rubber phase formed and only cloudy liquid came out of thereaction zone outlet (7). Upon the injection of acid into the reactionzone (13), a worm-like, semi-solid silica-containing continuous rubberphase started to form as the flow of acetic acid through the third inletwas increased from 0 L/hr to 60 L/hr. The materials flowing from theoutlet still contained a significant amount of cloudy liquid, indicatinga significant amount of waste. TGA analysis of the dried product showedthat the silica-containing continuous rubber phase formed in thisexperimental run only contained 25 phr silica. Based on the productionconditions selected and the amount of silica used, if the silica hadbeen substantially incorporated into the silica-containing rubber phaseas in Example 3-A, the silica would have yielded a silica-containingrubber phase comprising in excess of 50 phr silica.

These experiments show that the silica slurry must be destabilized priorto initial impact with the elastomer latex in order to achieve thedesired silica-containing, continuous rubber phase. Example 3-A achievedwhat was considered efficient capture of the silica within the solidsilica-containing, continuous rubber phase, whereas Example 3-Dillustrates a comparative process utilizing an initially stable silicaslurry and demonstrating less than half of the efficiency of Example 3-Autilizing an initially destabilized silica slurry. The observation of acloudy liquid exiting the reaction zone exit point indicatesinsufficient mixing of the silica with the latex and a lower proportionof silica captured within the continuous rubber phase. It is theorizedthat in comparative processes 3B and 3D, there was insufficientdestabilization of fluids during mixing. The results further show thatpoor capture of silica occurs when additional fluid is added while thefirst fluid and second fluid are being mixed together, and such processconditions generate unwanted amounts of waste.

Example 4

In these examples, the process according to various embodiments of theinvention was run in the apparatus shown in either FIG. 1A or 1B undervarious conditions as described in Table 4, utilizing either Process Aor Process B described above. Operating conditions were selected toyield a solid or semi-solid silica-containing, continuous rubber phasewith the silica to rubber ratios set forth in Table 4.

TABLE 4 Silica^(a) Rubber Salt concentration Content in Latexconcentration Zeta in Latex wt % in Potential Process Slurry Latex (DRC)NH₃ Salt Slurry (Est.)^(b) Example A/B (wt %) Type (wt %) (wt %) Type(wt %) (mV) 4-1 A 20 Conc. 31.9 0.53 Ca(NO₃)₂ 1.0 −12.2 4-2 B 25 Conc.31 0.27 Ca(NO₃)₂ 0.75 −13.9 4-3 B 25 Field 33 0.60 N/A 0.00 −10.5 4-4 A18.5 Conc. 31 0.70 Ca(NO₃)₂ 0.75 −14.1 4-5 A 18.5 Conc. 30.6 0.70Ca(NO₃)₂ 0.39 −18.4 4-6 B 20 Conc. 31 0.27 Ca(NO₃)₂ 1 −1.8 4-7 A 20.0Conc. 31.9 0.53 Ca(NO₃)₂ 1 −12.2 4-8 A 10.0 Conc. 31.9 0.53 Ca(NO₃)₂ 0.5−17.1 4-9 A 10.0 Conc. 31.9 0.53 Ca(NO₃)₂ 0.5 −17.1 4-10 A 20.0 Field32.7 0.35 Ca(NO₃)₂ 1 −12.2 4-11 A 20.0 Field 32.7 0.35 Ca(NO₃)₂ 1 −12.24-12 A 20.0 Field 32.7 0.35 Ca(NO₃)₂ 1.3 −10.6 4-13 A 10.0 Field 32.70.35 Ca(NO₃)₂ 0.65 −15.4 4-14 A 10.0 Field 32.7 0.35 Ca(NO₃)₂ 0.65 −15.44-15 A 20.0 Conc. 31.9 0.53 N/A 0 −15.1 4-16 A 10.0 Conc. 31.9 0.53Ca(NO₃)₂ 0.55 −6.6 4-17 A 20.0 Field 32.7 0.33 N/A 0 −17.6 4-18 A 20.0Field 32.7 0.33 N/A 0 −17.6 4-19 A 20.0 Field 32.7 0.33 Ca(NO₃)₂ 1 −6.14-20 A 20.0 Field 32.7 0.33 Ca(NO₃)₂ 1 −6.1 4-21 A 20.0 Field 32.7 0.33Ca(NO₃)₂ 1 −6.1 4-22 A 16.0 Conc. 31.9 0.53 Ca(NO₃)₂ 1 −1.8 4-23 B 25Conc. 31 0.27 CaCl₂ 0.60 −12.8 4-24 B 25 Conc. 31 0.27 N/A 0 −10.6 4-25B 25 Conc. 31 0.27 N/A 0 −10.4 4-26 A 19.6 Field 32.8 0.66 Ca(NO₃)₂ 0.90−12.9 4-27 A 19.6 Field 32.8 0.66 Ca(NO₃)₂ 0.90 −12.9 4-28 B 25 Conc.30.5 0.27 Ca(NO₃)₂ 0.75 −13.9 4-29 B 25 Field 33.0 0.60 N/A 0.00 −9.84-30 B 25 Conc. 31.0 0.27 CaCl₂ 1.50 −6.9 4-31 B 25 Field 33.0 0.60 N/A0.00 −7.7 4-32 B 25 Conc. 31 0.27 N/A 0.00 −10.6 4-33 B 25 Conc. 31 0.27N/A 0.00 −10.4 4-34 B 25 Conc. 31.0 0.27 CaCl₂ 1.00 −9.5 4-35 A 18.5Conc. 30.6 0.70 Ca(NO₃)₂ 0.22 −22.0 4-36 B 25 Conc. 31 0.60 N/A 0.00−13.7 4-37 B 25 Conc. 31.0 0.27 Ca(NO₃)₂ 0.52 −12.8 4-38 A 15.0 Field32.8 0.66 N/A 0.00 −11.3 4-39 A 16.5 Conc. 30.6 0.68 N/A 0.00 −16.5 4-40B 25 Conc. 30.9 0.30 Al₂(SO₄)₃ 1.04 −5.0 4-41 B 15 Conc. 30.5 0.27 N/A0.00 −20.0 4-42 B 25 Conc. 30.5 0.27 Ca(NO₃)₂ 0.59 −3.0 4-43 B 25 Conc.31 0.27 Ca(NO₃)₂ 1.00 −12.1 N/A = not applicable Acid Slurry- wt % InletActual Slurry Latex to-Latex in Acid/NH₃ Nozzle Silica Flow Flow FlowAcid Slurry molar Velocity^(c) loading Rate^(d) Rate^(d) Ratio ExampleType (wt %) ratio (m/s) (phr) (L/hr) (L/hr) (v/v) 4-1 N/A 0 0.00 49 38.4540 703 0.77 4-2 N/A 0 0.00 75 86.3 60 59 1.01 4-3 Formic 2.5 1.45 11 6960 76 0.79 4-4 N/A 0 0 50 26 788 1541 0.51 4-5 N/A 0 0 47 45.6 827 11120.74 4-6 N/A 0 0.00 76 49.2 60 56 0.94 4-7 N/A 0 0.00 75 54.8 828 5931.40 4-8 N/A 0 0.00 78 29.5 950 805 1.18 4-9 N/A 0 0.00 78 63.6 950 3792.51 4-10 N/A 0 0.00 76 45.4 738 794 0.93 4-11 N/A 0 0.00 76 76.9 738491 1.50 4-12 N/A 0 0.00 76 38.2 738 938 0.79 4-13 N/A 0 0.00 78 52 950484 1.96 4-14 N/A 0 0.00 78 77.8 950 300 3.17 4-15 Acetic 4.70 4.01 7525.4 828 593 1.40 4-16 Acetic 2.35 3.21 78 18.1 950 403 2.36 4-17 Acetic2.80 3.14 75 54.8 945 826 1.14 4-18 Acetic 2.80 3.93 75 67.2 945 6601.43 4-19 Acetic 2.8 1.77 76 54.9 963 841 1.14 4-20 Acetic 2.8 2.36 7643.3 630 734 0.86 4-21 Acetic 2.8 1.77 76 34.0 630 978 0.64 4-22 N/A 00.00 117 46.6 966 773 1.25 4-23 N/A 0 0.00 75 50.4 60 68 0.88 4-24Formic 2.5 2.93 6475 60 5160 81 0.74 4-25 Formic 2.6 2.34 75 47 60 1030.58 4-26 N/A 0 0.00 103 110 1639 827 1.98 4-27 N/A 0 0.00 119 175 1902648 2.94 4-28 N/A 0 0.00 75 86.3 60 59 1.01 4-29 Formic 3.2 1.45 21 9760 97 0.62 4-30 N/A 0 0 19 138 60 43 1.38 4-31 Formic 7.1 1.45 29 27 60214 0.28 4-32 Formic 2.5 4.19 75 ND 60 57 1.06 4-33 Formic 2.6 4.26 75ND 60 57 1.06 4-34 N/A 0 0.00 19 122 60 37 1.63 4-35 N/A 0 0.00 87 ND1090 932 1.17 4-36 acetic 6.2 1.82 64 58 60 114 0.53 4-37 formic 0.91.47 29 ND 60 57 1.06 4-38 formic 2.0 1.59 41 44 800 626 1.28 4-39acetic 3.6 1.81 64 40.4 800 743 1.08 4-40 N/A 0 0.00 29 ND 60 88 0.684-41 acetic 1.8 4.11 77 29 60 30 2.02 4-42 N/A 0 0 75 70.9 60 58 1.044-43 N/A 0 0 75 ND 60 142 0.42 ND = not determined, N/A= not applicable.^(c)The inlet nozzle velocity is the velocity of the silica slurry as itpasses through a nozzle (3a) at first inlet (3) to the reaction zone(13) prior to contacting the latex. ^(d)Slurry and Latex Flow Rates arethe volumetric flow rates in L/hour of the silica slurry and the latexfluid, respectively, as they are delivered to the reaction zone.

-   -   a. Examples 4-6 and 4-22 used Agilon 454 silica (precipitated        silica treated with silane coupling agents, obtained from PPG        Industries Inc.). Examples 4-24 and 4-32 used Zeosil® 175GR        silica (conventional precipitated silica, obtained from Solvay        S.A.). Examples 4-25 and 4-33 used Zeosil® Premium 200MP silica        (HDS with high surface area of 200 m²/g, obtained from Solvay        S.A.). Example 4-41 used Hi-Sil® 243LD silica (obtained from PPG        Industries Inc, and Example 4-42 used Agilon 400 silica        (obtained from PPG Industries Inc). All other examples used        ZEOSIL® Z1165 MP precipitated silica. Example 4-38 included 1.5        wt % (on a total slurry weight basis) N134 carbon black (Cabot        Corporation) in the silica slurry.    -   b. Zeta potential values were estimated by interpolation of        experimentally determined curves of zeta potential dependence on        concentration of the salt or the acid of the slurries of the        same grade of silica.

In all the examples except Examples 4-13 and 4-14, the selectedoperating conditions yielded a solid silica-containing, continuousrubber phase in a roughly cylindrical form. The product contained amajor amount of water, was elastic and compressible, and expelled waterand retained solids content when manually compressed. The solid materialcould be stretched, for example, the material of example 4-17 could bestretched or elongated to 130-150% of its original length, withoutbreaking. Silica particles were observed to be uniformly distributedthroughout a continuous rubber phase and this product was substantiallydevoid of free silica particles and larger silica grains, both onexterior and interior surfaces. In some of the examples (4-13 and 4-14),the selected operating conditions yielded a semi-solid product with apaste-like consistency, comprising a semi-solid silica-containing,continuous rubber phase. Silica particles were observed, on visualexamination, to be entrapped within, and uniformly distributedthroughout, the rubber phase. The semi-solid material expelled water andretained solids content upon further processing in one or moresubsequent operations selected to develop the paste-like material into asolid silica-containing continuous rubber phase. For the solid orsemi-solid silica-containing, continuous rubber phase to form, not onlydid the silica need to be destabilized (e.g., by prior treatment withacids and/or salts), but the volumetric flow rates of destabilizedsilica slurry relative to the latex had to be adjusted not only forachieving a desired silica to rubber ratio (phr) in the elastomercomposite, but also for balancing the degree of slurry destabilizationto the rate of slurry and latex mixing and the rate of coagulation oflatex rubber particles. By means of such adjustments, as the silicaslurry entrained the latex, intimately distributing silica particlesinto the rubber, the rubber in the latex became a solid or semi-solidcontinuous phase, all within a fraction of a second after combining thefluids in the confined volume of the reaction zone. Thus, the processformed unique silica elastomer composites by means of a continuous fluidimpact step done with sufficient velocity, selected fluid solidsconcentrations and volumes, and adjusted fluid flow rates to uniformlyand intimately distribute the fine particulate silica within the latexand, in parallel, as such distribution occurs, to cause a liquid tosolid phase inversion of the rubber.

Comparative Example 5

In these comparative examples, the same basic steps and apparatus asdescribed for Example 4 were used, but the combination of processconditions selected for each of the comparative examples in Table 5failed to create a solid or semi-solid continuous rubber phase, and asilica elastomer composite could not be produced. Table 5 below setsforth the concentration of silica in the slurry and the concentration ofacetic acid or calcium nitrate, if any, and other details of theseexamples.

TABLE 5 Acetic Silica Rubber Salt Acid concen- content concen- concen-tration of Latex tration tration Acid/ in Latex wt % in in NH₃Comparative Process Slurry Latex (DRC) NH₃ Salt Slurry Slurry molarExample A/B (wt %) Type (wt %) (wt %) Type (wt %) (wt %) ratio 5-1 A18.5 Conc. 30.6 0.70 Ca(NO₃)₂ 0.22 N/A 0 5-2 A 18.5 Conc. 30.6 0.70Ca(NO₃)₂ 0.48 N/A 0 5-3 A 20.0 Field 32.7 0.35 Ca(NO₃)₂ 1 N/A 0 5-4 A20.0 Field 32.7 0.35 Ca(NO₃)₂ 1.3 N/A 0 5-5 A 10.0 Field 32.7 0.35Ca(NO₃)₂ 0.65 N/A 0 5-6 A 20.0 Conc. 31.9 0.53 N/A 0 4.70 0.66 5-7 A20.0 Field 32.7 0.33 N/A 0 2.80 0.98 5-8 B 25 Conc. 31 0.27 N/A 0 0 0.005-9 A 18.5 Conc. 30.6 0.70 N/A 0 0 0.00 5-10 A 18.5 Conc. 30.6 0.70 N/A0 0 0.00 5-11 B 20 Conc. 30.5 0.27 N/A 0 0 0.00 5-12 A 16.0 Conc. 31.90.53 N/A 0 0 0.00 Zeta Inlet Slurry Slurry to Potential NozzleSilica/Rubber Flow Latex Flow Latex Flow Comparative (Est.)^(a)velocity^(b) ratio setting Rate^(c) Rate^(c) Ratio Example (mV) (m/s)(phr) (L/hr) (L/hr) (v/v) 5-1 −22.0 65 50 818 1118 0.73 5-2 −17.0 50 30792 1807 0.44 5-3 −12.2 76 40 738 1289 0.57 5-4 −10.6 76 40 738 12890.57 5-5 −15.4 78 60 950 524 1.81 5-6 −15.1 76 20 630 2255 0.28 5-7−17.6 76 25 630 1761 0.36 5-8 −32.0 75 50 60 114 0.53 5-9 −37 82 30 7921807 0.44 5-10 −37 85 50 818 1118 0.73 5-11 −4.8 76 70 60 64 0.94 5-12−7.9 67 50 552 619 0.89 N/A = not applicable. ^(a)Zeta potential valueswere estimated by interpolation of experimentally determined curves ofzeta potential dependence on concentration of the salt or the acid ofthe slurries of the same grade of silica. ^(b)The inlet nozzle velocityis the velocity of the silica slurry as it passes through a nozzle (3a)at first inlet (3) to the reaction zone prior to contacting the latex.^(c)Slurry and Latex Flow Rates are the volumetric flow rates in L/hourof the silica slurry and the latex fluid, respectively, as they aredelivered to the reaction zone. ^(d)Examples 5-11 and 5-12 used Agilon ®454 silica.

Comparative Examples 5-8, 5-9, and 5-10 show that withoutpre-destabilization of silica in the slurry, no silica-containingcontinuous rubber phase was produced, even when using the remainingprocess steps according to embodiments of the present invention.

Comparative Examples 5-1, 5-2, 5-3, 5-4, 5-5, 5-6 and 5-7 show that evenwith prior destabilization of silica in the slurry (zeta potential ofsilica below 25 mV), a silica-containing continuous rubber phase couldnot be made with the combination of relative volumetric flow rates anddegree of dilution of the destabilization agent, (e.g., Ca(NO₃)₂ oracetic acid) in the reaction zone when fluids were mixed. Without beingbound to any theory, it is theorized that such a low concentration ofthe destabilization agent in the mixture of slurry and latex in thereaction zone may reduce the coagulation rate of latex rubber particlesso that a continuous rubber phase could not be formed within the shortresidence time in the reaction zone. In the Comparative Example 5-1,with 18.5 wt % of destabilized silica slurry and 30.6 wt % DRC latexconcentrate, a relative flow ratio of destabilized slurry to latex wasset at 0.73 (V/V) to deliver a silica to rubber ratio of 50 phr to thereaction zone. It is theorized that latex rubber particles did notcoagulate within the 0.48 second residence time of the mixture in thereaction zone at such relatively low volumetric flow ratio ofdestabilized slurry to latex, whereby the original concentration ofCa(NO₃)₂ of 14.8 mM in the destabilized silica slurry was diluted by 58%to 6.2 mM in the reaction zone. Thus, it was not possible under theseconditions to produce a solid or semi-solid silica-containing,continuous rubber phase comprising 50 phr silica. However, when a highersalt concentration (e.g., 0.5 wt % for Invention Example 4-8 versus 0.22wt % for Comparative Example 5-1) was used (zeta potential of −17.1 mVversus −22 mV), and the volumetric flow ratio of slurry to latex was setat 0.73 to produce 50 phr silica-containing rubber, suitable product wasmade. Comparative Example 5-3 shows that a solid silica-containing,continuous rubber phase could not be made at settings of 40 phr silicaand a volumetric flow ratio of destabilized slurry to field latex of0.57 (V/V), whereas such products were made when the flow ratio was 0.93and 1.50 thereby forming elastomer composite with 45.4 phr and 76.9 phrsilica, respectively, (Invention Examples 4-10 and 4-11). The higherslurry-to-latex volumetric flow ratios in the Inventive Examples 4-10and 4-11 led to less dilution of the salt in the reaction zone than inthe Comparative Example 5-3, thus producing a solid silica-containing,continuous rubber phase.

The salt concentration in the 18.5% destabilized silica slurry ofComparative Example 5-2 was 0.48%, with a zeta potential of −17 mV,indicating a degree of destabilization on par with those of InventionExamples 4-4 (−14.1 mV) and 4-5 (−18.4 mV), but no solidsilica-containing, continuous rubber phase was formed at a productionsetting of 30 phr silica content with latex concentrate at therelatively low flow ratio of selected for Comparative Example 5-2.Without wishing to be bound by any theory, it is believed that too muchdilution of the salt and/or destabilized silica slurry by latexconcentrate in the reaction zone in the Comparative Example 5-2 reducedthe coagulation rate of the rubber latex particles in the reaction zoneso much that a coherent continuous rubber phase would not form in theresidence time of 0.36 seconds within the reaction zone.

When mixing field latex with a 10 wt % silica slurry destabilized by0.65% Ca(NO₃)₂ (zeta potential at −15.4 mV), Comparative Example 5-5 didnot produce a solid silica-containing, continuous rubber phase at asilica to rubber ratio of 60 phr and slurry-to-latex volumetric flowratio of 0.57. These conditions did not deliver sufficient salt and/ordestabilized slurry to the reaction zone for rapid coagulation of therubber latex particles within the reaction zone. In general, either thedegree of silica slurry destabilization and/or slurry-to-latex flowratio adequate to coagulate latex concentrate were not sufficient tocoagulate field latex.

Similar results were obtained when acid was employed to destabilize thesilica slurry of Comparative Examples 5-6 and 5-7 and Invention Example4-17, respectively. When acid was used as the sole agent to destabilizethe silica slurry, there was a preferred threshold acid-to-ammonia molarratio in the mixture of the slurry and latex in the reaction zone, belowwhich solid or semi-solid silica-containing continuous rubber phasewould not form in the reaction zone. In these experiments, the thresholdacid-to-ammonia molar ratio that is desired was always higher than 1.0,with the result that the pH of the product exiting the reaction zone wasacidic. In the case of Comparative Examples 5-6 and 5-7, forsilica-to-rubber ratio production settings of 20 phr and 25 phr,relatively low slurry-to-latex volumetric flow ratios of 0.28 and 0.36were used, respectively. At these low flow ratios, the acidic slurry wasnot sufficiently acidic to neutralize the ammonia in the latex. Theacid-to-ammonia molar ratios for Comparative Examples 5-6 and 5-7 were0.66 and 0.98, respectively. In both cases, only cloudy liquid sprayedout of the reaction zone. In contrast, for the Invention Example 4-17, ahigher slurry-to-latex volumetric flow ratio of 1.14 was used forachieving 54.8 phr silica loading, through delivering sufficient acidfrom slurry into the reaction zone for neutralizing ammonia from latex.The acid-to-ammonia molar ratio in the reaction zone for the InventionExamples 4-17 was 3.14, and a solid silica-containing, continuous rubberphase was produced as an elastic worm-like material exiting the reactionzone. This material could be stretched to 130-150% of its originallength without breaking.

Example 6

To explore the process variables that enable formation of a solid orsemi-solid silica-containing continuous rubber phase, a series ofexperiments were conducted under various combinations of processvariables, including, but not limited to, concentration of silica in thedestabilized slurry, concentration of acid or salts in the destabilizedslurry, types of latex (e.g. field latex and latex concentrate),concentration of ammonia in latex, latex lots, flow rates ofdestabilized slurry and latex, velocities of destabilized slurry andlatex in reaction zone, and acid or salt concentrations in reactionzone. This series of experiments was carried out according to Process A,and calcium nitrate was used as the salt. The solid contents of fluidsand the inlet nozzle velocities for the experiments are listed in Tables6 and 7 for a latex concentrate and field latex, respectively. At a lowslurry to latex volumetric flow ratio (i.e., low silica to rubber ratioin the reaction zone), the destabilized slurry and salt were diluted bythe latex, and no solid or semi-solid silica-containing continuousrubber phase was formed. The setting for silica to rubber ratio was thengradually increased by raising the slurry-to-latex volumetric flow ratiountil a solid or semi-solid silica-containing, continuous rubber phasewas observed exiting the reaction zone. In Tables 6 and 7, the “SilicaLoading Delivered to Reaction Zone” indicates the lowestsilica-to-rubber ratio at which a solid or semi-solid silica-containing,continuous rubber phase was produced. The minimum salt concentration inthe reaction zone (including both destabilized slurry and latex) forformation of solid or semi-solid silica-containing, continuous rubberphase was calculated for each set of experimental conditions (e.g.,silica concentration in slurry, salt concentration in slurry, slurryvelocity). For the first six examples listed in Table 6, the silicaconcentration in the destabilized slurry was the same, namely 18.5 wt %,but the salt concentration in the destabilized slurry was varied, andthe silica loading lower threshold for formation of a solid orsemi-solid silica-containing, continuous rubber phase was determined ineach example by increasing the latex volumetric flow rate until coagulumwas formed. Results in Table 6 show that, when the salt concentration inthe destabilized silica slurry was increased from 0.22 wt % to 0.75 wt%, it was possible to reduce the slurry-to-latex volumetric flow ratio,so as to obtain a solid or semi-solid silica-containing, continuousrubber phase having a lower silica to rubber ratio. For instance, byincreasing the salt concentration from 0.22 wt % to 0.65 wt % of a 18.5wt % silica slurry, the minimum silica phr setting for creating a solidor semi-solid silica-containing continuous rubber phase decreased from80 phr silica to 35 phr silica as the relative volumetric flow of latexwas increased and the ratio of slurry-to-latex volumetric flow rates wasdecreased from 1.17 to 0.51. Similar results were observed for othersilica slurry concentrations and when acid was used to destabilize thesilica slurry.

Table 6. Solid or semi-solid silica-containing continuous rubber phaseformation thresholds: phr silica loading and calcium nitrateconcentration under various conditions when destabilized silica slurrywas mixed with 50% diluted latex concentrate (31 wt % dry rubbercontent; 0.70 wt % ammonia content except for last sample, for whichammonia content was 0.53 wt %) using Process A.

TABLE 6 Silica Zeta Loading Slurry Silica Po- Delivered to [Ca²⁺] Conc.[Ca²⁺] ten- Inlet to latex Conc in In Ca(NO₃)₂ in tial Nozzle Reactionflow Reaction Slurry in Slurry slurry (Est.) Velocity Zone ratio Zone(wt %) (wt %) (mM) (mV) (m/s)^(a) (phr) (v/v) (mM) 18.5 0.22 14.8 −22.087 80 1.17 7.9 18.5 0.39 26.2 −18.4 46 46.3 0.68 10.5 18.5 0.48 32.3−17.0 67 40 0.59 11.9 18.5 0.52 34.9 −16.5 58 45 0.66 13.8 18.5 0.6543.6 −15.1 58 35 0.51 14.7 18.5 0.75 50.4 −14.1 59 35 0.51 17.0 26 0.6847.6 −14.5 54 55 0.55 16.8 26 0.99 69.3 −12.1 77 50 0.50 23.0 11 0.3623.2 −19.1 80 35 0.90 10.9 20 1.00 67.8 −12.2 49 35 0.49 22.2 ^(a)Theinlet nozzle velocity is the velocity of the silica slurry as it passesthrough a nozzle (3a) at first inlet (3) to the reaction zone prior tocontacting the latex.

Table 7. Solid or semi-solid silica-containing continuous rubber phaseformation thresholds: phr silica loading and calcium nitrateconcentration under various conditions when silica slurry was mixed withfield latex using Process A.

TABLE 7 [Ca²⁺] Silica Silica Slur- Conc Conc. Zeta Inlet Loading ry inIn [Ca²⁺] Poten- Nozzle Lower to Reac- Slur- Ca(NO₃)₂ in tial Ve-Thresh- latex tion ry in Slurry slurry Slurry locity old ratio Zone (wt%) (wt %) (mM) (mV) (m/s)^(a) (phr) (v/v) (mM) 10 0.65 41.7 −15.4 78 651.96 27.6 19.6 0.90 60.8 −12.9 71 65 0.95 29.6 20 1.0 67.7 −12.2 76 650.93 32.6 20 1.3 88.0 −10.6 76 50 0.72 36.7 ^(a)The inlet nozzlevelocity is the velocity of the silica slurry as it passes through anozzle (3a) at first inlet (3) to the reaction zone prior to contactingthe latex.

In a batch mode coagulation experiment conducted by mixing silica slurrywith latex in a bucket under relatively low shear mixing, the minimumamount of the salt or acid to coagulate the latex in the mixture is aconstant, independent of original concentration of salt or acid in thesilica slurry before mixing. However, in processes according to variousembodiments of the invention, the threshold concentration of the salt inthe reaction zone for formation of a solid or semi-solidsilica-containing, continuous rubber phase increases with increases inthe salt concentration in the destabilized silica slurry before mixing(i.e. the degree of destabilization of silica slurry). For example, inTable 6, one can see that the threshold concentration of Ca(NO₃)₂ forcoagulating the latex concentrate is independent of silica concentrationin the destabilized slurry, but depends strongly on the original saltconcentration in the destabilized silica slurry. When the saltconcentration increased from 14.8 mM to 69.3 mM, the threshold saltconcentration increased from 7.9 mM to 23.0 mM. For comparison, a seriesof batch coagulation experiments were conducted in a bucket using lowshear stirring and it was determined that the threshold concentration ofCa(NO₃)₂ for coagulating the same latex concentrate was a constant at10.7 mM, independent of both the original salt concentration in thedestabilized silica slurry as well as the silica concentration in thedestabilized slurry. These results highlight the importance of balancingthe degree of destabilization of the silica slurry, rate of mixing, rateof silica particle agglomeration, and rate of latex coagulation underhigh shear for efficiently producing a solid or semi-solidsilica-containing, continuous rubber phase.

Likewise, the threshold acid-to-ammonia ratio for formation of a solidor semi-solid silica-containing, continuous rubber phase according toembodiments of the invention is not a constant, but increases with thedegree of acid destabilization of the silica slurry.

Based on the production variables described herein, such as the velocityof the destabilized silica slurry, the velocity of the latex, therelative flow rates of the destabilized silica slurry and latex fluids,the degree of destabilization of the silica slurry, the silicaconcentration in the destabilized slurry, the dry rubber content of thelatex, and the ammonia concentration of the latex (e.g., the ammoniaconcentration can be reduced by bubbling nitrogen through the latex oron top of the liquid surface), it was possible to obtain and/or predictformation of a solid or semi-solid silica-containing, continuous rubberphase over a range of desired silica loadings. Thus, the process of theinvention can be operated over an optimized range of variables.

Comparative Example 7

The following comparative experiments utilizing a multi-step batchprocess were conducted as a comparison to a continuous process accordingto embodiments of the invention.

In these comparative examples, a slurry of silica was combined withelastomer latex under batch mixing conditions, using either a silicaslurry that had been ground (as in the process of Process B above), or asilica slurry prepared without grinding, each at two slurryconcentrations: 25 wt % and 6 wt %, respectively (based on the totalweight of the slurry). The silica used in these examples was ZEOSIL®1165 MP. The elastomer latex used in all experiments was high ammonialatex concentrate (60CX12021, from Chemionics Corporation, Tallmadge,Ohio) diluted by 50% (by weight) with deionized water.

Experiment 7-A: Batch Mixing with Ground Silica Slurry.

The silica slurry prepared above was mixed with a desired amount ofdeionized water in a 5 gallon bucket to achieve the target silicaconcentration of slurry.

For each run described below, the indicated quantity of silica slurrywas taken from the slurry run tank and mixed for fifteen minutes withthe indicated quantity of elastomer latex in a 5 gallon bucket—using anoverhead low shear stirrer (Model #1750, Arrow Engineering Co, Inc.,Hillside, N.J.). Except in Run 5, calcium chloride salt was then addedto the mixture and mixing continued until coagulation appeared to becomplete. Unless otherwise indicated, the salt was added as a 20 wt %salt solution in deionized water. The amount of salt used (dry amount)is indicated below. The “target phr silica” reflects the amount ofsilica in phr expected to be present in the rubber composite based onthe starting amount of silica used, assuming all silica was incorporatedinto all of the rubber. Runs 1-4 were dewatered and dried according tothe Process B methods described above.

Run 1—Target 55 phr silica rubber composite using 25 wt % silica slurry.

-   -   Conditions (for approx. 1.9 kg dried material):        -   2.7 kg of 25 wt % silica slurry, ground        -   4.0 kg of latex concentrate        -   0.060 kg (equivalent dry amount) of salt in solution.

Observations: Big pieces of wet rubber composite were formed around themixing blade after coagulation was complete. However, coagulation didnot incorporate all of the rubber and silica into the coagulum, as amilky liquid remained in the mixing bucket and a layer of wet silica wasdeposited on the bottom of the bucket. The dried coagulum weighed about0.5 kg, which was much less than the 1.9 kg targeted yield. Asignificant amount of silica appeared on the surface of the rubberproduct indicating poor distribution of silica within the rubbercomposite. The silica appeared to be very poorly mixed with rubber inthe coagulum, and undispersed grains of silica were felt and seenthroughout the coagulum. Silica particles were observed falling offdried coagulum. When dry rubber product was cut using a pair ofscissors, silica particles fell from the cut surface. Following drying,TGA analysis of the rubber product indicated loadings of silica averagedabout 44 phr.

Run 2—Target 70 phr silica rubber composite using 25 wt % silica slurry.

-   -   Conditions (for approx. 1.9 kg dried material):        -   3.1 kg of 25 wt % silica slurry, ground        -   3.6 kg of latex concentrate        -   0.060 kg of salt, added dry.

Observations: Big pieces of wet rubber were formed around the mixingblade and the post coagulation liquid was cloudy or milky. A layer ofsilica remained on the bottom of the bucket. Approximately 1 kg of driedcoagulum was produced. Similar to Run 1, very poor distribution ofsilica particles within the rubber coagulum was observed. Followingdrying, TGA analysis of the rubber product revealed silica loadingsaveraging about 53 phr.

Run 3—Target 55 phr silica rubber composite using 6 wt % silica slurry.

-   -   Conditions (for approx. 2 kg dried material):        -   2.6 kg of 25 wt % silica slurry, ground        -   8.4 kg deionized water        -   4.0 kg of latex concentrate        -   0.090 kg of salt in solution.

Observations: After adding the salt, the whole mixture of latex andslurry became a soft gel. About 0.9 kg dry composite was made. Similarto Run 1, very poor distribution of silica particles within the rubbercoagulum was observed. Following drying, the silica loading in thecoagulum measured by TGA was about 45 phr.

Run 4—Target 70 phr silica rubber composite using 6 wt % silica slurry.

-   -   Conditions (for approx. 2 kg dried material):        -   3.1 kg of 25 wt % silica slurry, ground        -   9.9 kg water        -   3.7 kg of latex concentrate        -   0.10 kg of salt in solution.

Observations: After adding the salt, small crumbs formed in milkyliquid. A sieve was used to collect and compact the small crumbs.Similar to Run 1, very poor dispersion of silica particles within therubber coagulum was observed. About 0.7 kg dry composite was collectedwith silica loading in the crumb measured by TGA at about 50 phr.

Run 5 Target 55 phr silica rubber composite using 25 wt % silica slurrydestabilized with 1% of CaCl₂.

-   -   Conditions (for approx. 1.9 kg dried material):        -   4.0 kg of 25 wt % slurry containing 1% CaCl₂, ground        -   2.7 kg latex concentrate.

Observations: The latex was put in a 5-gallon bucket with an overheadlow shear stir. The ground 25% destabilized silica slurry containing 1%of CaCl₂ was poured into the bucket with stirring, and stirringcontinued until coagulation was complete. Visual and tactileobservations of the rubber piece revealed many large pockets (mm to cmsize) of silica slurry within the rubber piece and a large quantity ofsilica particles trapped but not distributed within the solid rubberphase. The average silica loading in the dried coagulum measured by TGAwas about 58 phr. Sample-to-sample variations of silica loadings weregreater than 10 phr.

Experiment 7-B: Batch Mixing Using Silica Slurry Without Grinding.

For preparing the silica slurry without grinding, the silica was slowlyadded to water using only an overhead stirrer (Model #1750, ArrowEngineering Co, Inc., Hillside, N.J.). When the silica appeared to becompletely dispersed, the latex was added and the liquid mixture stirredfor 20 minutes. The CaCl₂ salt solution was then added to the liquidmixture and allowed to mix until coagulation appeared to be complete.Samples were dried in an oven prior to TGA analysis.

Run 5B—Target 65 phr silica rubber composition using 25 wt % silicaslurry.

-   -   Conditions (for approx. 1.9 kg dried material):        -   3.0 kg of 25 wt % silica slurry        -   3.8 kg of latex concentrate        -   0.06 kg of salt in solution.

Observations: After adding the salt, very large pieces of rubbercoagulum were formed around the blade of the stirrer. After coagulation,a thick layer of silica settled at the bottom of the bucket. The rubberpiece felt gritty and slimy. Grains of silica could be felt and seen onthe surface of the rubber coagulum and visual observation revealed verypoor distribution of silica in the rubber coagulum. The silica loadingin the coagulum was determined as 25 phr using TGA.

Run 6—Target 80 phr silica rubber composite using 25 wt % silica slurry.

-   -   Conditions (for approx. 1.9 kg dried material):        -   3.3 kg of 25 wt % silica slurry        -   3.4 kg of latex concentrate        -   0.06 kg of salt in solution.

Observations: The loading of silica in the rubber was determined as 35phr and visual observation revealed very poor distribution of silica inthe rubber coagulum.

Run 7—Target 110 phr silica rubber composite using 6 wt % silica slurry.

-   -   Conditions (for approx. 1.9 kg dried material, done in two        batches):        -   1.0 kg of 25 wt % silica slurry        -   15.6 kg of water        -   3.0 kg of latex concentrate        -   0.120 kg of salt in solution.

Observations: Small rubber crumbs were formed in the bucket and theliquid remaining after coagulation was mostly clear, with a layer ofsilica on the bottom of the bucket. TGA measured silica loading in therubber product averaged about 30 phr. The coagulum was elastic, withsilica grains on the surface. As it dried, silica could easily bebrushed off the surface, and visual observation revealed very poordistribution of silica in the rubber coagulum.

Run 8—Target 140 phr silica rubber composite using 6 wt % silica slurry.

-   -   Conditions (for approx. 1.9 kg dried material, done in two        batches):        -   1.0 kg of 25 wt % silica slurry        -   15.7 kg of water        -   2.4 kg of latex concentrate        -   0.110 kg of salt in solution.

Observations: Small rubber crumbs were formed in the bucket and theliquid remainder after coagulation was mostly clear, with a layer ofsilica on the bottom of the bucket. TGA measured silica loading in therubber product averaged about 35 phr. Particles of silica were settledon the surface of the rubber product that could be brushed free as itdried, and visual observation revealed very poor distribution of silicain the rubber coagulum.

Summary of Observations. Compared with the continuous process of makingelastomer composite, as for instance in Examples 4 and 6, batch latexmixing process of Example 7 were incapable of achieving the desiredquality or quantity of silica dispersion in rubber. With ground silicaslurries, the actual silica loading in rubber products produced withbatch mixing was observed to be <55 phr. After coagulation, asignificant amount of silica settled at the bottom of the mixing bucketand appeared on the surface of the rubber product , indicating poorcapture of silica particles within the rubber coagulum. With silicaslurries that had not been ground, the actual silica loading in rubberproduced with batch mixing was limited to 30 phr to 35 phr. Aftercoagulation, a thick layer of silica settled at the bottom of the mixingbucket, the silica appeared to be very poorly mixed with rubber in thecoagulum, and undispersed grains of silica were felt and seen throughoutthe coagulum. Compared to processes according to embodiments of thepresent invention, batch mixing processes yielded poor incorporation anddistribution of silica particles within the rubber matrix of thecoagulum. In the product of each of these batch mixing runs, silicaparticles were observed falling off dried coagulum. When dry rubbercomposite was cut using a pair of scissors, silica particles fell fromthe cut surface. Such loss of silica particles was not observed inexamining the solid or semi-solid silica-containing continuous rubberphase produced by processes according to embodiments of the invention.

The present invention includes the followingaspects/embodiments/features in any order and/or in any combination:

A method of producing a silica elastomer composite, comprising:

-   -   (a) providing a continuous flow under pressure of at least a        first fluid comprising a destabilized dispersion of particulate        silica and a continuous flow of at least a second fluid        comprising elastomer latex;    -   (b) providing volumetric flow of the first fluid relative to        that of the second fluid to yield an elastomer composite having        a silica content of about 15 phr to about 180 phr;    -   (c) combining the first fluid flow and the second fluid flow        with a sufficiently energetic impact to distribute the        particulate silica within the elastomer latex to obtain a flow        of a solid or semi-solid silica elastomer composite comprising a        continuous phase of rubber with dispersed silica particles.

The method of any preceding or following embodiment/feature/aspect:

-   -   wherein said flow of said solid or semi-solid silica elastomer        composite forms in two seconds or less after combining said        first fluid flow and second fluid flow, or    -   wherein said flow of said solid or semi-solid silica elastomer        composite forms in about 50 milliseconds to about 1500        milliseconds after combining said first fluid flow and second        fluid flow, or    -   wherein said first fluid in step (a) further comprises at least        one salt, or    -   wherein said first fluid in step (a) further comprises at least        one acid, or    -   wherein said solid or semi-solid silica elastomer composite        comprises a discontinuous phase of from about 40 wt % to about        95 wt % water or aqueous fluid, or    -   wherein said combining occurs in a reaction zone having a volume        of about 10 cc to about 500 cc, or    -   wherein the relative volumetric flows are at a volumetric flow        ratio of first fluid to second fluid of from 0.4:1 to 3.2:1, or    -   wherein the relative volumetric flows are at a volumetric flow        ratio of first fluid to second fluid of from 0.2:1 to 2.8:1, or    -   wherein the relative volumetric flows are at a volumetric flow        ratio of first fluid to second fluid of from 0.4:1 to 3.2:1, and        said destabilized dispersion of particulate silica includes at        least one salt, or    -   wherein the relative volumetric flows are at a volumetric flow        ratio of first fluid to second fluid of from 0.2:1 to 2.8:1, and        said destabilized dispersion of particulate silica includes at        least one acid, or    -   wherein said elastomer latex comprises a base, said destabilized        dispersion of particulate silica comprises at least one acid,        and a molar ratio of hydrogen ions in said acid in said first        fluid to said base in said second fluid is at least 1.0, or    -   wherein said elastomer latex comprises a base, said destabilized        dispersion of particulate silica comprises at least one acid,        and a molar ratio of hydrogen ions in said acid in said first        fluid to said base in said second fluid is at least 1.1, or    -   wherein said elastomer latex comprises a base, said destabilized        dispersion of particulate silica comprises at least one acid,        and a molar ratio of hydrogen ions in said acid in said first        fluid to said base in said second fluid is at least 1.2, or    -   wherein said elastomer latex comprises a base, said destabilized        dispersion of particulate silica comprises at least one acid,        and a molar ratio of hydrogen ions in said acid in said first        fluid to said base in said second fluid is from 1 to 4.5, or    -   wherein said destabilized dispersion of particulate silica        comprises at least one acid, and wherein said elastomer latex        present in said second fluid has an ammonia concentration of        from about 0.3 wt % to about 0.7 wt % based on the weight of the        elastomer latex, and a molar ratio of hydrogen ions in said acid        in said first fluid to ammonia in said second fluid is at least        1.0 to 1.0, or    -   wherein said silica content of said silica elastomer composite        is from about 25 phr to about 80 phr, or    -   wherein said silica content of said silica elastomer composite        is from about 40 phr to about 115 phr, or    -   wherein said destabilized dispersion of particulate silica        comprises about 6 wt % to about 35 wt % silica, or    -   wherein said destabilized dispersion of particulate silica        comprises about 10 wt % to about 28 wt % silica, or    -   further comprising recovering said solid or semi-solid silica        elastomer composite at ambient pressure, or    -   wherein said first fluid comprising said destabilized dispersion        of particulate silica has a zeta potential magnitude of less        than 30 mV, or    -   wherein said first fluid comprising said destabilized dispersion        of particulate silica has a zeta potential magnitude of 28 mV or        less, or    -   wherein said first fluid comprising said destabilized dispersion        of particulate silica has a zeta potential magnitude of about 29        mV to about 5 mV, or    -   wherein said first fluid comprising said destabilized dispersion        of particulate silica has a zeta potential magnitude of about 20        mV to about 1 mV, or    -   wherein said destabilized dispersion of particulate silica        includes at least one salt, wherein salt ion concentration in        said destabilized dispersion is from about 10 mM to about 160        mM, or    -   wherein said destabilized dispersion of particulate silica        includes at least one salt, wherein said salt is present in said        destabilized dispersion in an amount of from about 0.2 wt % to        about 2 wt % based on weight of said destabilized dispersion, or    -   wherein said destabilized dispersion of particulate silica        includes at least one acid, wherein said acid is present in said        destabilized dispersion in an amount of from about 0.8 wt % to        about 7.5 wt % based on weight of said destabilized dispersion,        or    -   wherein said destabilized dispersion of particulate silica        includes at least one acid, wherein acid concentration in said        destabilized dispersion is from about 200 mM to about 1000 mM,        or    -   wherein step (c) is carried out with the continuous flow of the        first fluid at a velocity A and the continuous flow of the        second fluid at a velocity B, and velocity A is at least 2 times        faster than velocity B, or    -   wherein step (c) is carried out in a semi-confined reaction zone        and the first fluid has a velocity sufficient to induce        cavitation in the reaction zone upon combining with the second        fluid, or    -   wherein the second fluid has a velocity sufficient to create        turbulent flow, or    -   wherein said dispersion of particulate silica comprises a        surface-modified particulate silica having hydrophobic surface        moieties, or    -   wherein said first fluid is an aqueous fluid, or    -   wherein said first fluid comprises an aqueous fluid and about 6        wt % to about 35 wt % particulate silica, or    -   wherein said first fluid is an aqueous fluid, further comprising        at least one salt, and at least one acid, or    -   wherein carbon black is present in said silica elastomer        composite in an amount of from about 10 wt % to about 0.1 wt %        based on total particulates present in said silica elastomer        composite, or    -   wherein carbon black is present in said silica elastomer        composite in an amount of 10 wt % or less, based on total        particulates present in said silica elastomer composite, or    -   said method further comprising destabilizing a dispersion of        particulate silica by lowering a pH of the dispersion of        particulate silica so as to form the destabilized dispersion of        particulate silica provided in step (a), or    -   said method further comprising destabilizing a dispersion of        particulate silica by lowering a pH of the dispersion of        particulate silica to a pH of from 2 to 4 so as to form the        destabilized dispersion of particulate silica provided in step        (a), or    -   wherein said particulate silica has a hydrophilic surface, or        wherein said particulate silica is a highly dispersible silica        (HDS), or    -   wherein wherein said acid comprises at least one organic acid,        or    -   wherein said acid comprises acetic acid, formic acid, citric        acid, phosphoric acid, or sulfuric acid, or any combinations        thereof, or    -   wherein said acid comprises a C₁ to C₄ alkyl containing acid, or    -   wherein said acid has a molecular weight or an average molecular        weight below 200, or    -   wherein said salt comprises at least one alkali metal salt, or    -   wherein said salt comprises a calcium salt, magnesium salt, or        aluminum salt, or a combination thereof, or    -   said method further comprising subjecting particulate silica to        mechanical processing to yield a reduced particle size, or    -   wherein wherein said mechanical processing comprises grinding,        milling, commutation, bashing, or high shear fluid processing,        or any combinations thereof, or    -   wherein the particulate silica is precipitated silica or fumed        silica or colloidal silica, or any combinations thereof, or    -   wherein said particulate silica is silica with BET surface area        of from about 20 m²/g to about 450 m²/g, or    -   wherein said elastomer latex is natural rubber latex, or    -   wherein said the natural rubber latex is in the form of a field        latex, latex concentrate, desludged latex, chemically modified        latex, enzymatically modified latex, or any combinations        thereof, or    -   wherein said the natural rubber latex is in the form of an        epoxidized natural rubber latex, or    -   wherein said the natural rubber latex is in the form of a latex        concentrate, or    -   further comprising mixing the silica elastomer composite with        additional elastomer to form an elastomer composite blend.

A method for making a rubber compound comprising

-   -   (a) conducting the method of any preceding or following        embodiment/feature/aspect, and    -   (b) blending the silica elastomer composite with other        components to form the rubber compound, wherein said other        components comprise at least one antioxidant, sulfur, polymer        other than an elastomer latex, catalyst, extender oil, resin,        coupling agent, one or more additional elastomer composite(s),        or reinforcing filler, or any combinations thereof.

A method for making a rubber article selected from tires, moldings,mounts, liners, conveyors, seals, or jackets, comprising

-   -   (a) conducting the method of any preceding or following        embodiment/feature/aspect, and    -   (b) compounding the silica elastomer composite with other        components to form a compound, and    -   (c) vulcanizing the compound to form said rubber article.

The method of any preceding or following embodiment/feature/aspect,further comprising conducting one or more post processing steps afterrecovering the silica elastomer composite.

The method of any preceding or following embodiment/feature/aspect,wherein the post processing steps comprise at least one of:

-   -   a) dewatering the silica elastomer composite to obtain a        dewatered mixture;    -   b) mixing or compounding the dewatered mixture to obtain a        compounded silica elastomer composite;    -   c) milling the compounded silica elastomer composite to obtain a        milled silica elastomer composite;    -   d) granulating or mixing the milled silica elastomer composite;    -   e) baling the silica elastomer composite after the granulating        or mixing to obtain a baled silica elastomer composite;    -   f) extruding the silica elastomer composite;    -   g) calendaring the silica elastomer composite; and/or    -   h) optionally breaking apart the baled silica elastomer        composite and mixing with further components.

The method of any preceding or following embodiment/feature/aspect:

-   -   wherein the post processing steps comprise at least roll milling        of the silica elastomer composite, or    -   wherein the post processing steps comprise compressing the        silica elastomer composite to remove from about 1 wt % to about        15 wt % of the discontinuous aqueous fluid phase, or    -   wherein the elastomer latex is brought into contact with at        least one destabilizing agent as the destabilized dispersion of        particulate silica is combined with the elastomer latex, or    -   further comprising bringing the flow of solid or semi-solid        silica elastomer composite into contact with at least one        destabilizing agent, or    -   further comprising the step of conducting one or more of the        following with the solid or semi-solid silica elastomer        composite:    -   a) transferring the solid or semi-solid silica elastomer        composite to a holding tank or container;    -   b) heating the solid or semi-solid silica elastomer composite to        reduce water content;    -   c) subjecting the solid or semi-solid silica elastomer composite        to an acid bath;    -   d) mechanically working the solid or semi-solid silica elastomer        composite to reduce water content, or    -   wherein said silica elastomer composite is a semi-solid silica        elastomer composite, and said method further comprising        converting said semi-solid silica elastomer composite to a solid        silica elastomer composite, or    -   wherein said semi-solid silica elastomer composite is converted        to said solid silica elastomer composite by treatment with an        aqueous fluid comprising at least one acid, or at least one        salt, or a combination of at least one acid and at least one        salt, or    -   wherein said second fluid comprises a blend of two or more        different elastomer latices, or    -   wherein said process further comprises providing one or more        additional fluids and combining the one or more additional        fluids with said first fluid flow and second fluid flow, wherein        said one or more additional fluids comprise one or more        elastomer latex fluids, and said additional fluids are the same        as or different from said elastomer latex present in said second        fluid flow.

The present invention can include any combination of these variousfeatures or embodiments above and/or below as set forth in any sentencesand/or paragraphs herein. Any combination of disclosed features hereinis considered part of the present invention and no limitation isintended with respect to combinable features.

Applicants specifically incorporate the entire contents of all citedreferences in this disclosure. Further, when an amount, concentration,or other value or parameter is given as either a range, preferred range,or a list of upper preferable values and lower preferable values, thisis to be understood as specifically disclosing all ranges formed fromany pair of any upper range limit or preferred value and any lower rangelimit or preferred value, regardless of whether ranges are separatelydisclosed. Where a range of numerical values is recited herein, unlessotherwise stated, the range is intended to include the endpointsthereof, and all integers and fractions within the range. It is notintended that the scope of the invention be limited to the specificvalues recited when defining a range.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalents thereof.

What is claimed is:
 1. A method of producing a silica elastomer composite, comprising: (a) providing a continuous flow under pressure of at least a first fluid comprising a destabilized dispersion of silica and a continuous flow of at least a second fluid comprising elastomer latex; (b) providing volumetric flow of the first fluid relative to that of the second fluid to yield a silica content of about 15 phr to about 180 phr in the silica elastomer composite; (c) combining the first fluid flow and the second fluid flow with a sufficiently energetic impact to distribute the silica within the elastomer latex to obtain a flow of a solid silica-containing continuous rubber phase or semi-solid silica-containing continuous rubber phase .
 2. The method of claim 1, wherein said flow of said solid or semi-solid silica-containing continuous rubber phase forms in two seconds or less after combining said first fluid flow and second fluid flow.
 3. The method of claim 1, wherein said flow of said solid or semi-solid silica-containing continuous rubber phase forms in about 50 milliseconds to about 1500 milliseconds after combining said first fluid flow and second fluid flow.
 4. The method of claim 1, wherein said first fluid in step (a) further comprises at least one salt.
 5. The method of claim 1, wherein said first fluid in step (a) further comprises at least one acid.
 6. The method of claim 1, wherein said solid or semi-solid silica-containing continuous rubber phase comprises from about 40 wt % to about 95 wt % water or aqueous fluid.
 7. The method of claim 1, wherein said combining occurs in a reaction zone having a volume of about 10 cc to about 500 cc.
 8. The method of claim 1, where the relative volumetric flows are at a volumetric flow ratio of first fluid to second fluid of from 0.4:1 to 3.2:1.
 9. The method of claim 1, where the relative volumetric flows are at a volumetric flow ratio of first fluid to second fluid of from 0.2:1 to 2.8:1.
 10. The method of claim 1, wherein the relative volumetric flows are at a volumetric flow ratio of first fluid to second fluid of from 0.4:1 to 3.2:1, and said destabilized dispersion of silica includes at least one salt.
 11. The method of claim 1, wherein the relative volumetric flows are at a volumetric flow ratio of first fluid to second fluid of from 0.2:1 to 2.8:1, and said destabilized dispersion of silica includes at least one acid.
 12. The method of claim 1, wherein said elastomer latex comprises a base, said destabilized dispersion of silica comprises at least one acid, and a molar ratio of hydrogen ions in said acid in said first fluid to said base in said second fluid is from 1 to 4.5.
 13. The method of claim 1, wherein said destabilized dispersion of silica comprises at least one acid, and wherein said elastomer latex present in said second fluid has an ammonia concentration of from about 0.3 wt % to about 0.7 wt % based on the weight of the elastomer latex, and a molar ratio of hydrogen ions in said acid in said first fluid to ammonia in said second fluid is at least 1:1.
 14. The method of claim 1, wherein said silica content of said silica elastomer composite is from about 35 phr to about 115 phr.
 15. The method of claim 1, wherein said silica content of said silica elastomer composite is from about 40 phr to about 115 phr.
 16. The method of claim 1, wherein said destabilized dispersion of silica comprises about 6 wt % to about 35 wt % silica.
 17. The method of claim 1, wherein said destabilized dispersion of silica comprises about 10 wt % to about 28 wt % silica.
 18. The method of claim 1, further comprising recovering said solid or semi-solid silica-containing continuous rubber phase at ambient pressure.
 19. The method of claim 1, wherein said first fluid comprising said destabilized dispersion of silica has a zeta potential magnitude of less than 30 mV.
 20. The method of claim 1, wherein said destabilized dispersion of silica includes at least one salt, wherein salt ion concentration in said destabilized dispersion is from about 10 mM to about 160 mM.
 21. The method of claim 1, wherein said destabilized dispersion of silica includes at least one salt, wherein said salt is present in said destabilized dispersion in an amount of from about 0.2 wt % to about 2 wt % based on weight of said destabilized dispersion.
 22. The method of claim 1, wherein said destabilized dispersion of silica includes at least one acid, wherein said acid is present in said destabilized dispersion in an amount of from about 0.8 wt % to about 7.5 wt % based on weight of said destabilized dispersion.
 23. The method of claim 1, wherein said destabilized dispersion of silica includes at least one acid, wherein acid concentration in said destabilized dispersion is from about 200 mM to about 1000 mM.
 24. The method of claim 1, wherein step (c) is carried out with the continuous flow of the first fluid at a velocity A and the continuous flow of the second fluid at a velocity B, and velocity A is at least 2 times faster than velocity B.
 25. The method of claim 1, wherein step (c) is carried out in a semi-confined reaction zone and the first fluid has a velocity sufficient to induce cavitation in the reaction zone upon combining with the second fluid.
 26. The method of claim 25, wherein the second fluid has a velocity sufficient to create turbulent flow.
 27. The method of claim 1, wherein said dispersion of silica comprises a surface-modified silica having hydrophobic surface moieties.
 28. The method of claim 1, wherein said first fluid comprises an aqueous fluid.
 29. The method of claim 1, wherein said first fluid comprises an aqueous fluid and about 6 wt % to about 35 wt % silica.
 30. The method of claim 1, wherein said first fluid comprises an aqueous fluid, further comprising at least one salt, and at least one acid.
 31. The method of claim 1, wherein carbon black is present in said silica elastomer composite in an amount of from about 10 wt % to about 0.1 wt % based on total particulates present in said silica elastomer composite.
 32. The method of claim 1, said method further comprising destabilizing a dispersion of silica by lowering a pH of the dispersion of silica so as to form the destabilized dispersion of silica provided in step (a).
 33. The method of claim 1, said method further comprising destabilizing a dispersion of silica by lowering a pH of the dispersion of silica to a pH of from 2 to 4 so as to form the destabilized dispersion of silica provided in step (a).
 34. The method of claim 1, wherein said silica has a hydrophilic surface.
 35. The method of claim 1, wherein said silica is a highly dispersible silica (HDS).
 36. The method of claim 5, wherein said acid comprises acetic acid, formic acid, citric acid, phosphoric acid, or sulfuric acid, or any combinations thereof.
 37. The method of claim 5, wherein said acid has a molecular weight or an average molecular weight below
 200. 38. The method of claim 4, wherein said salt comprises at least one Group 1, 2, or 13 metal salt.
 39. The method of claim 4, wherein said salt comprises a calcium salt, magnesium salt, or aluminum salt, or a combination thereof.
 40. The method of claim 1, said method further comprising subjecting silica to mechanical processing to yield a reduced particle size.
 41. The method of claim 1, wherein the silica is precipitated silica or fumed silica or colloidal silica, or any combinations thereof.
 42. The method of claim 1, wherein said silica has a BET surface area of from about 20 m²/g to about 450 m²/g.
 43. The method of claim 1, wherein said elastomer latex is natural rubber latex.
 44. The method of claim 43, wherein said the natural rubber latex is in the form of a field latex, latex concentrate, desludged latex, chemically modified latex, enzymatically modified latex, or any combinations thereof.
 45. The method of claim 43, wherein said the natural rubber latex is in the form of an epoxidized natural rubber latex.
 46. The method of claim 43, wherein said the natural rubber latex is in the form of a latex concentrate.
 47. The method of claim 1, further comprising mixing the silica elastomer composite with additional elastomer to form an elastomer composite blend.
 48. A method for making a rubber compound comprising (a) conducting the method of claim 1, and (b) blending the silica elastomer composite with other components to form the rubber compound, wherein said other components comprise at least one antioxidant, sulfur, polymer other than an elastomer latex, catalyst, extender oil, resin, coupling agent, one or more additional elastomer composite(s), or reinforcing filler, or any combinations thereof.
 49. A method for making a rubber article selected from tires, moldings, mounts, liners, conveyors, seals, or jackets, comprising (a) conducting the method of claim 1, and (b) compounding the silica elastomer composite with other components to form a compound, and (c) vulcanizing the compound to form said rubber article.
 50. The method of claim 1, further comprising conducting one or more post processing steps after recovering the silica elastomer composite.
 51. The method of claim 50, wherein the post processing steps comprise at least one of: a) dewatering the silica elastomer composite to obtain a dewatered mixture; b) mixing or compounding the dewatered mixture to obtain a compounded silica elastomer composite; c) milling the compounded silica elastomer composite to obtain a milled silica elastomer composite; d) granulating or mixing the milled silica elastomer composite; e) baling the silica elastomer composite after the granulating or mixing to obtain a baled silica elastomer composite; f) extruding the silica elastomer composite; g) calendaring the silica elastomer composite; and/or p1 h) optionally breaking apart the baled silica elastomer composite and mixing with further components.
 52. The method of claim 50, wherein the post processing steps comprise at least roll milling of the silica elastomer composite.
 53. The method of claim 50, wherein the post processing steps comprise compressing the solid or semi-solid silica-containing continuous rubber phase to remove from about 1 wt % to about 15 wt % of aqueous fluid contained therein.
 54. The method of claim 1, wherein the elastomer latex is brought into contact with at least one destabilizing agent as the destabilized dispersion of silica is combined with the elastomer latex.
 55. The method of claim 1, further comprising bringing the flow of solid or semi-solid silica-containing continuous rubber phase into contact with at least one destabilizing agent.
 56. The method of claim 1, further comprising the step of conducting one or more of the following with the solid or semi-solid silica-containing continuous rubber phase: a) transferring the solid or semi-solid silica-containing continuous rubber phase to a holding tank or container; b) heating the solid or semi-solid silica-containing continuous rubber phase to reduce water content; c) subjecting the solid or semi-solid silica-containing continuous rubber phase to an acid bath; d) mechanically working the solid or semi-solid silica-containing continuous rubber phase to reduce water content.
 57. The method of claim 1, wherein said silica elastomer composite is a semi-solid silica-containing continuous rubber phase, and said method further comprising converting said semi-solid silica-containing continuous rubber phase to a solid silica-containing continuous rubber phase.
 58. The method of claim 57, wherein said semi-solid silica-containing continuous rubber phase is converted to said solid silica-containing continuous rubber phase by treatment with an aqueous fluid comprising at least one acid, or at least one salt, or a combination of at least one acid and at least one salt.
 59. The method of claim 1, wherein said second fluid comprises a blend of two or more different elastomer latices.
 60. The method of claim 1, wherein said process further comprises providing one or more additional fluids and combining the one or more additional fluids with said first fluid flow and second fluid flow, wherein said one or more additional fluids comprise one or more elastomer latex fluids, and said additional fluids are the same as or different from said elastomer latex present in said second fluid flow.
 61. The method of claim 1, wherein said silica content of said silica elastomer composite is about 35 phr to about 180 phr.
 62. A solid silica-containing continuous rubber phase article comprising at least 40 parts per hundred of rubber (phr) of silica dispersed in natural rubber and at least 40 wt % aqueous fluid, and having a length dimension (L), wherein the solid silica-containing continuous rubber phase article can be stretched to 130-150% of (L) without breaking. 